Photo-curable adhesive sheet, photo-curable transfer sheet, optical information recording medium, and method for preparing optical information recording medium

ABSTRACT

A process for the preparation of an optical information recording medium comprises superposing two optical information recording substrates having an uneven surface of recorded pits and/or grooves on each other through a photo-curable adhesive sheet comprising a photo-curable composition which comprises a reactive polymer having a photopolymerizable functional group and Tg of not more than 20° C., the photo-curable adhesive sheet having a light transmittance of not less than 70% in a wavelength range of 380 to 420 nm, such that the two uneven surfaces face each other, depressing the substrates and sheet to form a laminate, and curing the laminate by light. A process for the preparation of an optical information recording medium comprises placing a photo-curable transfer sheet comprising a photo-curable composition which comprises a reactive polymer having a photopolymerizable functional group and Tg of not more than 20° C. on an optical information recording substrate having an uneven surface of recorded pits and/or grooves such that one side of the photo-curable transfer sheet is in contact with the uneven surface of the optical information recording substrate, depressing the sheet and substrate to form a laminate in which the one side of the photo-curable transfer sheet adheres closely to the uneven surface, and exposing the photo-curable transfer sheet of the laminate to ultraviolet rays to cure the transfer sheet. A photo-curable transfer sheet comprises a photo-curable composition which comprises a reactive polymer having a photopolymerizable functional group and which is capable of deforming by application of pressure, at least one side of the photo-curable transfer sheet having a surface roughness (Ra) of not more than 30 nm.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to an optical information recordingmedium, such as DVD (Digital Versatile Disc), CD (Compact Disc), anoptical magnetic disc or a hard disc, in which a large amount ofinformation such as letters, sound and animation is recorded and/orrecordable as digital signals, and a process for the preparationthereof, and further a photo-curable adhesive sheet and a photo-curabletransfer sheet in the preparation of the medium.

2. Description of the Related Art

As an optical information recording medium in which digital signals havebeen already recorded by forming pits on its surface, CD and CD-ROM arewidely used. Recently, DVD that animation can be also recorded byforming pits on its both (double) sides has been noted as the nextgeneration recording medium instead of CD and increasingly used.Further, attention is directed to recordable discs such as CD-R, DVD-Rand DVD-RW having groove(s) or grooves and pits thereon. Furthermore, anoptical magnetic disc and a hard disc are also well known as therecordable disc.

Conventional DVD having recording layers on its both sides includes adisc readable from double sides, as shown in, for example, FIG. 12, inwhich each of reflective layers 1 a, 2 a is formed on a surface ofsignal-pits of each of transparent resin substrates 1, 2 having thesurface of signal-pits on its one side, and the two transparent resinsubstrates 1, 2 are bonded to each other through an adhesive layer 3such that the reflective layers 1 a, 2 a face each other; and a discreadable from single side, as shown in, for example, FIG. 13, in which asemitransparent reflective layers 1 b is formed on a surface ofsignal-pits of one transparent resin substrate 1 while a reflectivelayers 2 a is formed on a surface of signal-pits of another transparentresin substrate 2 and the two transparent resin substrates 1, 2 arebonded to each other through an adhesive layer 3 such that thesemitransparent reflective layers 1 b and the reflective layer 2 a faceeach other.

The DVD readable from double sides can be prepared, for example, bysubjecting melted polycarbonate resin to injection molding by the use ofa stamper having unevenness (concave and convex) corresponding to thereverse of unevenness of the signal-pit to be recorded on the substrateto prepare a transparent resin substrate having unevenness on itssurface, forming a reflective layer on the uneven surface by spatteringmetal such as aluminum on it, and bonding two transparent resinsubstrates obtained in the above manner to each other through anadhesive such that the two reflective layers face each other. Theadhesive usually uses an ultraviolet (UV) curable resin in the form ofliquid.

The preparation of the optical information recording medium such as DVDusually requires an adhesive step for bonding two transparent resinsubstrates as mentioned above. Since the optical information recordingmedium is recorded and read out by light, a substrate of the medium isneeded to have a uniform thickness and high transparency, and be freefrom deformation such as warpage. When the liquid UV curable resin isused as an adhesive, the resultant adhesive layer has high transparencybut is apt to have warpage due to large shrinkage on curing, whichpossibly results on reduction of dimensional stability.

JA11-273147 describes that a pressure-sensitive adhesive sheet or a dryphotopolymer in addition to the liquid UV curable resin is used forbonding a transparent film to an injection molded substrate having anuneven surface. However, the publication describes that the dryphotopolymer is not preferred due to its low transparency.

With increase of information to be recorded, a new optical informationrecording medium, which has lager storage capacity than DVD now on use,is proposed. To obtain the large storage capacity, it is required to notonly reduce sizes of signal pits and a groove but also shorten awavelength of recording or reading laser. Further the shortening of thewavelength reduces distance between the laser and a surface having thepits and therefore it is needed to reduce a thickness of the opticalrecording substrate. Hence, it is also preferred to reduce a thicknessof the adhesive layer.

For example, a standardized specification of a next generation opticaldisc “Blue-Ray Disc” was proposed on Feb. 10, 2002. The specificationmainly includes storage capacity of 23.3/25/27 GB, laser wavelength of405 nm (violaceous laser), lens numerical aperture (N/A) of 0.85, discdiameter of 120 mm, disc thickness of 1.2 mm and track pitch of 0.32 μm.

In the Blue-Ray Disc, as mentioned above, the sizes of groove and pitsare reduced, and therefore it is required to reduce a spot size of areading laser. The reduction of the spot size results in that thereading is apt to be influenced by inclination of the disc, and henceeven DVD having a little warpage cannot be reproduced (read out). Inorder to avoid the disadvantage, it may be effective to reduce athickness of a substrate and make a thickness of a cover layer providedon pits surface on a laser-irradiation side to approx. 0.1 mm.

“NIKKEI ELECTRONICS, Nov.” 5, 2001, pp. 68 describes a process for thepreparation of DVD suited to the above-mentioned requirements. Theprocerss is explained by referring to FIG. 14. A UV curable resin 5A isprovided, by application, on a reflective layer (or recording layer) 6 aof a disc substrate (0.1 mm) 4 a having the reflective layer on itsuneven surface, while a UV curable resin 5B is provided, by application,on a stamper 4 b made of polycarbonate having uneven surface.Subsequently, after the substrate is turned over, the turned-oversubstrate and the stamper are put together, and the UV curable resins5A, 5B are cured by irradiating ultraviolet beam from the stamper side.The stamper 4 b is then removed from the cured UV curable resin 5B, areflective layer (or recording layer) 6 b is formed on the unevensurface and further a cover layer (thickness of approx. 0.1 mm) 7 isprovided the reflective layer 6 b.

SUMMARY OF THE INVENTION

To achieve a new optical information recording medium having lagerstorage capacity than DVD now on use, the present inventors have made anenthusiastic study. A first aspect according to the present invention ismade in view of the disadvantage of the above-mentioned adhesive, andhence the object of the first invention is to provide a photo curableadhesive sheet that can be advantageously used in the preparation of anoptical information recording medium.

Further, the object of the first aspect is to provide a photo curableadhesive sheet that can be advantageously used in the preparation of anoptical information recording medium having good dimensional stabilityand high transparency.

Furthermore, the object of the first aspect is to provide a process forthe preparation of an optical information recording medium by using thephoto curable adhesive sheet.

In the process described in NIKKEI ELECTRONICS, a UV curable resin(layer) is provided on a disc substrate and a stamper by application,and the substrate is turned over and bonded to the stumper. Hence, theprocess is needed to perform complicated procedures such as theapplication and turning over steps. In more detail, when the turned-oversubstrate and the stamper are put together through UV curable resins,bubbles are generated in the vicinity of an interface of the combined UVcurable resins. Hence it is difficult to successfully bond the UVcurable resins of the substrate and stamper to each other. Furthermore,the UV curable resin is accompanied by large shrinkage on its curing,and hence the resultant medium is apt to have deformation such aswarpage.

In view of the above-mentioned problems, the object of a second aspectof the invention is to provide a process for preparing extremely easilyan optical information recording medium in high productivity, which isuseful for forming on a disc substrate having an uneven surface a layerhaving an uneven surface (i.e., another uneven surface).

Further, the object of a second aspect of the invention is to provide aprocess for the preparation of an optical information recording mediumwhich is capable of transferring easily and precisely an uneven surfaceof a disc substrate.

Furthermore, the object of a second aspect of the invention is toprovide a process for the preparation of an optical informationrecording medium which is capable of transferring successively, easilyand precisely an uneven surface of a disc substrate and an unevensurface of a stamper.

Moreover, the object of a second aspect of the invention is to providean optical information recording medium scarcely having deformation suchas warpage which can be obtained by the above-mentioned process.

Further, the object of a second aspect of the invention is to provide anoptical information recording medium having precisely transferredunevenness and excellent smooth surface, especially an opticalinformation recording medium having a reduced thickness.

As mentioned above, though a transparent resin substrate (opticalinformation recording substrate) of DVD is prepared by injection moldingof polycarbonate, the formation of pits by the injection molding bringsabout reduction of precision of pit shape transferred from the stamperto the polycarbonate resin, particularly in case of a substrate havingthickness of 300 μm or less (see JA11-273147). Further, the presentinventors have found a problem that a land portion of the surface havingthe pits comes to rough.

The present applicant filled a patent application as to a photo-curabletransfer sheet having a little shrinkage on curing to which anunevenness surface of a stamper for preparing a substrate of an opticalinformation recording medium can be easily and precisely transferred bydepression, and especially by which a thin substrate having thickness of300 μm or less can be advantageously prepared (Patent Application No.2001-305946). The sheet is used in the above-mentioned process. Thoughthis sheet has a little shrinkage on curing, it does not occasionallyhave sufficiently excellent smooth surface. In more detail, a surfacehaving no unevenness of the substrate corresponds to a side irradiatedby a laser for recording and/or reading out, and therefore when thesurface is rough, errors are apt to occur in the operation for recordingand/or reading out.

In view of the above-mentioned problems, the object of a third aspect ofthe invention is to provide a photo-curable transfer sheet havingsufficiently an excellent smooth surface to which an uneven surface of astamper for preparing a substrate of an optical information recordingmedium can be easily and precisely transferred by depression, andespecially by which a thin substrate having thickness of 300 μm or lesscan be advantageously prepared.

Further, the object of a third aspect of the invention is to provide aprocess for the preparation of the above-mentioned photo-curabletransfer sheet.

Furthermore, the object of a third aspect of the invention is to providea photo-curable transfer sheet suitable for preparing an opticalinformation recording medium having one surface onto which unevenness ofa stamper is precisely transferred and the other surface havingexcellent smoothness (laser-irradiation side).

Moreover, the object of a third aspect of the invention is to provide aphoto-curable transfer sheet suitable for preparing an opticalinformation recording medium having precisely formed pit signals and/orgroove on one side (surface) and excellent smoothness on the other side(laser-irradiation side).

In the first to third aspects of the present invention, it is common torealize a new optical information recording medium having lager storagecapacity than DVD is common, and particularly common is the use of aspecific photo-curable composition comprising a reactive polymer havinga photopolymerizable functional group.

The first aspect is attained by a photo-curable adhesive sheetcomprising a photo-curable composition which comprises a reactivepolymer having a photopolymerizable functional group and weight-averagemolecular weight of not less than 5,000 and which has a glass transitiontemperature of not more than 20° C., the photo-curable adhesive sheethaving a light transmittance of not less than 70% in a wavelength rangeof 380 to 420 nm.

In the photo-curable adhesive sheet, the reactive polymer preferably hasa glass transition temperature of not more than 20° C., which rendersthe formation of unevenness by depression at room temperature easy. Thephoto-curable adhesive sheet preferably has a light transmittance of notless than 80% in a wavelength rang of 380 to 420 nm. Further, theadhesive sheet preferably has a light transmittance of not less than 70%in a wavelength rang of 380 to 600 nm, especially in a wavelength rangof 380 to 800 nm. It is ensured that an optical disc (opticalinformation recording medium) obtained by using the adhesive sheethaving the light transmittance is read out without error if the disc isdone by irradiation of laser. Moreover, the photo-curable adhesive sheetgenerally has cure shrinkage of not more than 8%.

Further, it is preferred that the reactive polymer is an acrylic resin.Further the reactive polymer preferably has 1 to 50% by mole of thephotopolymerizable functional group. The photopolymerizable functionalgroup generally is a (meth)acryloyl group. The preferred reactivepolymer is an acrylic resin having the photopolymerizable functionalgroup through a urethane bond. The photo-curable composition generallycontains 0.1 to 10% by weight of a photopolymerization initiator. Thephoto-curable adhesive sheet preferably has a thickness of 5 to 300 μm.It is preferred that a release sheet is provided on at least (especiallyboth sides) one side of the photo-curable adhesive sheet.

The first aspect of the invention is also provided by a process for thepreparation of an optical information recording medium comprising:

-   -   superposing two optical information recording substrates having        an uneven surface of recorded pits and/or grooves on each other        through the photo-curable adhesive sheet as defined in any of        claims 1 to 9 such that the two uneven surfaces face each other,    -   depressing the substrates and sheet to form a laminate, and        curing the laminate by light.

In the process, the depressing step is preferably carried out underreduced pressure, and the depressing step is also preferably carried outat room temperature.

The second aspect of the invention is provided by a process for thepreparation of an optical information recording medium comprising:

-   -   placing a photo-curable transfer sheet comprising a        photo-curable composition which comprises a reactive polymer        having a photopolymerizable functional group and weight-average        molecular weight of not less than 5,000 and which is capable of        deforming by application of pressure on an optical information        recording substrate having the uneven surface of recorded pits        and/or grooves such that one side of the photo-curable transfer        sheet is in contact with the uneven surface of the optical        information recording substrate,    -   depressing the sheet and substrate to form a laminate in which        the one side of the photo-curable transfer sheet closely adheres        to the uneven surface, and    -   exposing the photo-curable transfer sheet of the laminate to        ultraviolet rays to cure the transfer sheet.

In the process, the depressing step is generally carried out underreduced pressure, whereby generation of bubbles can be suppressed.Further a reflective layer is preferably provided on the uneven surfaceof the optical information recording substrate. A recording layer can beprovided instead of the reflective layer. In this case, a groove isgenerally formed instead of pits.

The second aspect of the invention is also provided by process for thepreparation of an optical information recording medium comprising:

-   -   placing a photo-curable transfer sheet comprising a        photo-curable composition which comprises a reactive polymer        having a photopolymerizable functional group and weight-average        molecular weight of not less than 5,000 and which is capable of        deforming by application of pressure on an optical information        recording substrate having an uneven surface of recorded pits        and/or grooves such that one side of the photo-curable transfer        sheet is in contact with the uneven surface of the optical        information recording substrate,    -   depressing the sheet and substrate to allow the one side of the        photo-curable transfer sheet to adhere closely to the uneven        surface,    -   placing a stamper having an uneven surface of recorded pits        and/or grooves on the photo-curable transfer sheet such that the        uneven surface of the stamper is in contact with a side having        no contact with the substrate of the photo-curable transfer        sheet,    -   depressing the substrate, transfer sheet and stamper to form a        laminate in which the side of the photo-curable transfer sheet        adheres closely to the uneven surface of the stamper,    -   exposing the photo-curable transfer sheet of the laminate to        ultraviolet rays to cure the transfer sheet, and    -   removing the stamper out of the laminate to form unevenness        (e.g., recording pits) on a surface of the cured photo-curable        transfer sheet.

In the process, it is preferred that an organic polymer film is furtherprovided on the (cured) surface having an unevenness of the curedphoto-curable transfer sheet through an adhesive layer. Moreover,another photo-curable transfer sheet can be further depressed on thecured surface having an unevenness of the cured photo-curable transfersheet and cured by exposing another transfer sheet to ultraviolet rays.It is preferred that a reflective layer has been provided on theunevenness surface of the substrate, and a semitransparent reflectivelayer is further provided on the surface having an unevenness of thecured photo-curable transfer sheet. The depressing step is preferablycarried out under reduced pressure.

In the process, the photo-curable composition of the photo-curabletransfer sheet preferably has a glass transition temperature of not morethan 20° C., which renders the formation of unevenness by depression atroom temperature easy. The photo-curable transfer sheet generally has alight transmittance of not less than 70% in a wavelength rang of 380 to420 nm, preferably in a wavelength rang of 380 to 600 nm, especially ina wavelength rang of 380 to 800 nm. It is ensured that an optical discobtained by using the transfer sheet having the light transmittance isread out without error if the disc is done by irradiation of laser.Moreover, the photo-curable transfer sheet generally has cure shrinkageof not more than 8%.

Further, the reactive polymer preferably has a glass transitiontemperature of not more than 20° C. Further the reactive polymerpreferably has 1 to 50% by mole of the photopolymerizable functionalgroup whereby appropriate curing property of the polymer or appropriatestrength of the cured polymer is ensured. The photopolymerizablefunctional group generally is a (meth)acryloyl group in terms ofcurability. The preferred reactive polymer is an acrylic resin havingthe photopolymerizable functional group through a urethane bond. Thephoto-curable composition generally contains 0.1 to 10% by weight of aphotopolymerization initiator. The photo-curable transfer sheetpreferably has a thickness of 1 to 1,200 μm, especially 5 to 300 μm interms of transferring properties and workability. It is preferred thatat least one side of the photo-curable transfer sheet preferably has asurface roughness (Ra) of not more than 30 nm, especially not more than10 nm.

The third aspect of the invention is provided by a photo-curabletransfer sheet comprising a photo-curable composition which comprises areactive polymer having a photopolymerizable functional group andweight-average molecular weight of not less than 5,000 and which iscapable of deforming by application of pressure, at least one side ofthe photo-curable transfer sheet having a surface roughness (Ra) of notmore than 30 nm (especially not more than 10 nm).

In the photo-curable transfer sheet, the photo-curable compositionpreferably has a glass transition temperature of not more than 20° C.,which makes the formation of unevenness by depression at roomtemperature easy. The photo-curable transfer sheet generally has a lighttransmittance of not less than 70% in a wavelength rang of 380 to 420nm, preferably in a wavelength rang of 380 to 600 nm, especially in awavelength rang of 380 to 800 nm. It is ensured that an optical discobtained by using the transfer sheet having the light transmittance isoperated without error if the disc is read out by irradiation of laser.Moreover, the photo-curable transfer sheet generally has cure shrinkageof not more than 8%.

Further, the reactive polymer preferably has 1 to 50% by mole of thephotopolymerizable functional group whereby appropriate curing propertyof the polymer or appropriate strength of the cured polymer is ensured.The preferred reactive polymer is an acrylic resin having thephotopolymerizable functional group through a urethane bond. Thephotopolymerizable functional group generally is a (meth)acryloyl groupin terms of curing property. The photo-curable composition generallycontains 0.1 to 10% by weight of a photopolymerization initiator. Thephoto-curable transfer sheet preferably has a thickness of 5 to 300 μmin terms of transferring properties and workability.

The photo-curable transfer sheet can be advantageously obtained by aprocess comprising:

-   -   melting a photo-curable composition which comprises a reactive        polymer having a photopolymerizable functional group and        weight-average molecular weight of not less than 5,000 and which        is capable of deforming by application of pressure, and casting        the melted composition onto an surface of a support, the surface        having a surface roughness (Ra) of not more than 30 nm; or    -   a process comprising:    -   applying a coating liquid containing a photo-curable composition        which comprises a reactive polymer having a photopolymerizable        functional group and weight-average molecular weight of not less        than 5,000 and which is capable of deforming by application of        pressure onto a surface of a support, the surface having a        surface roughness (Ra) of not more than 30 nm, and    -   drying a layer of the coating liquid.

In the third aspect of the present invention, a laminate in which astamper having an uneven surface of recorded pits and/or grooves issuperposed on the photo-curable transfer sheet such that the one side ofthe photo-curable transfer sheet adheres closely to the uneven surfacecan be advantageously obtained.

Further, the following articles can be advantageously obtained:

-   -   an optical information recording substrate comprising a cured        film of the photo-curable transfer sheet and having an uneven        surface of recorded pits and/or grooves on one side of the cured        layer, the uneven surface and a reverse surface (side) of the        cured layer having a surface roughness (Ra) of not more than 30        nm;    -   an optical information recording medium comprising an optical        information recording substrate having an uneven surface of        recorded pits and/or grooves and a reflective layer formed on        the uneven surface, and another optical information recording        substrate having an uneven surface of recorded pits and/or        grooves and a semitransparent reflective layer formed on the        uneven surface, both the substrates being bonded to each other        through an adhesive layer such that both the reflective layers        face each other,    -   wherein at least one of the optical information recording        substrates comprises a cured film of the photo-curable transfer        sheet, the uneven surface and a reversed surface (side) of the        cured layer having a surface roughness (Ra) of not more than 30        nm; and    -   an optical information recording medium comprising an optical        information recording substrate having an uneven surface of        recorded pits and/or grooves and a reflective layer formed on        the uneven surface, and another optical information recording        substrate having an uneven surface of recorded pits and/or        grooves and a semitransparent reflective layer formed on the        uneven surface, both the substrates being bonded to each other        through an adhesive layer such that a side having no reflective        layer of the former substrate faces the semitransparent        reflective layer of the latter substrate,    -   wherein at least one of the optical information recording        substrates comprises a cured film of the photo-curable transfer        sheet, the uneven surface and a reversed surface (side) of the        cured layer having a surface roughness (Ra) of not more than 30        nm.

Moreover, in the third aspect, the following articles can beadvantageously obtained:

-   -   an optical information recording substrate comprising a cured        layer of a photo-curable transfer sheet which comprises a        reactive polymer having a photopolymerizable functional group        and which is capable of deforming by application of pressure,        one side of the cured layer having an uneven surface of recorded        pits and/or grooves, wherein a coating layer of ultraviolet        curable resin is provided on the other side having no unevenness        of the cured layer and cured to form cured layer as a surface        smoothed layer which has a surface roughness (Ra) of not more        than 30 nm;    -   an optical information recording medium comprising an optical        information recording substrate having an uneven surface of        recorded pits and/or grooves and a reflective layer formed on        the uneven surface, and another optical information recording        substrate having an uneven surface of recorded pits and/or        grooves and a semitransparent reflective layer formed on the        uneven surface, both the substrates being bonded to each other        through an adhesive layer such that both the reflective layers        face each other,    -   wherein at least one of the optical information recording        substrates comprises a cured layer of the photo-curable transfer        sheet which comprises a reactive polymer having a        photopolymerizable functional group and weight-average molecular        weight of not less than 5,000 and is capable of deforming by        application of pressure, and    -   wherein a coating layer of ultraviolet curable resin is provided        on the other side having no unevenness of the cured layer by        application and cured to form a cured layer as a surface        smoothed layer which has a surface roughness (Ra) of not more        than 30 nm; and    -   an optical information recording medium comprising an optical        information recording substrate having an uneven surface of        recorded pits and/or grooves and a reflective layer formed on        the uneven surface, and another optical information recording        substrate having an uneven surface of recorded pits and/or        grooves and a semitransparent reflective layer formed on the        uneven surface, both the substrates being bonded to each other        through an adhesive layer such that a side having no reflective        layer of the former substrate faces the semitransparent        reflective layer of the latter substrate,    -   wherein a layer comprising at least uneven surface of at least        one of the optical information recording substrates comprises a        cured layer of the photo-curable transfer sheet which comprises        a reactive polymer having a photopolymerizable functional group        and weight-average molecular weight of not less than 5,000 and        is capable of deforming by application of pressure,    -   wherein a coating layer of ultraviolet curable resin is provided        on the other side having no unevenness of the cured layer by        application and cured to form a cured layer as a surface        smoothed layer which has a surface roughness (Ra) of not more        than 30 nm.

In the optical information recording medium, the surface roughness (Ra)preferably is not more than 10 nm. The photo-curable compositionpreferably has a glass transition temperature of not more than 20° C.The photo-curable transfer sheet generally has a light transmittance ofnot less than 70% in a wavelength rang of 380 to 420 nm, preferably in awavelength rang of 380 to 800 nm. Further, the reactive polymerpreferably has 1 to 50% by mole of the photopolymerizable functionalgroup. The preferred reactive polymer is an acrylic resin having thephotopolymerizable functional group through a urethane bond. Thephotopolymerizable functional group generally is a (meth)acryloyl group.The photo-curable composition generally contains 0.1 to 10% by weight ofa photopolymerization initiator. The photo-curable transfer sheetpreferably has a thickness of 5 to 3001 μm in terms of transferringproperties and workability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view showing an example of an embodiment of aphoto-curable adhesive sheet according to a first aspect of the presentinvention.

FIG. 2 is a section view showing an example of a process for thepreparation of the optical information recording medium according to thefirst aspect.

FIG. 3 is a section view showing another example of a process for thepreparation of the optical information recording medium according to thefirst aspect.

FIG. 4 is a schematic view for explaining a depressing method using adevice according to a double vacuum chamber system.

FIG. 5 is a section view showing an example of an embodiment of aphoto-curable transfer sheet used in a second aspect of the presentinvention.

FIG. 6 is a section view showing an example of a process for thepreparation of an optical information recording medium according to thesecond aspect.

FIG. 7 is a section view showing an example of an optical informationrecording medium according to the second aspect.

FIG. 8 is a section view showing examples of an embodiment of aphoto-curable transfer sheet according to a third aspect of the presentinvention.

FIG. 9 is a section view showing an example of a process for thepreparation of an optical information recording substrate and a laminateusing the photo-curable transfer sheet of the third aspect.

FIG. 10 is a section view showing an example of a process for thepreparation of an optical information recording medium using thephoto-curable transfer sheet of the third aspect.

FIG. 11 is a section view showing an example of another opticalinformation recording medium obtained by the process of the thirdaspect.

FIG. 11 is a section view showing an example of a conventional opticalinformation recording medium.

FIG. 12 is a section view showing another example of a conventionaloptical information recording medium.

FIG. 13 is a section view showing a procedure for preparing aconventional optical information recording medium described in NIKKEIELECTRONICS.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention are explained in detail by referring todrawings.

FIG. 1 is a section view showing an example of an embodiment of thephoto-curable adhesive sheet 11 according to the first aspect of thepresent invention. In FIG. 1, the photo-curable adhesive sheet 11 hasrelease sheets 12 a, 12 b on its both sides. The release sheet may beprovided only on one side of the photo-curable adhesive sheet, andotherwise may not be provided, depending on uses of the resultantoptical disc. The provision on the both sides is advantageous because itfacilitates the handling of the adhesive sheet.

The photo-curable adhesive sheet 11 is a layer that is capable ofdeforming precisely along an uneven surface of, for example, an opticalinformation substrate when the photo-curable adhesive sheet 11 isdepressed on the uneven surface, and is mainly composed of aphoto-curable composition which comprises a reactive polymer having aphotopolymerizable functional group and weight-average molecular weightof not less than 5,000 and which has a glass transition temperature ofnot more than 20° C. Further, the photo-curable adhesive sheet 11 has alight transmittance of not less than 70% in a wavelength range of 380 to420 nm such that information can be easily read out by a reading(reproduction) laser. The light transmittance is preferably not lessthan 80% in a wavelength range of 380 to 420 nm. Hence, an optical discobtained by using the adhesive sheet can be advantageously used in aprocess for reproducing pit signals by using a reproduction laser havinga laser wavelength in the range of 380 to 420 nm.

The photo-curable adhesive sheet of the invention has flexibility suchthat contact bonding can be carried out at room temperature as describedabove. Hence, the photo-curable adhesive sheet has excellent handling,and therefore can be widely used in not only information recording mediasuch as CD, DVD, CD-R, DVD-R and DVD-RW but also the other various uses.The photo-curable adhesive sheet can be particularly advantageously usedin uses requiring precise bonding, such as the preparation of anelectrical appliance, a furniture, an automobile, an instrument, asports equipment or packing materials.

The optical information recording medium can be prepared using the abovephoto-curable adhesive sheet, for example, as shown in FIG. 2.

The release sheet 12 a is removed from the photo-curable adhesive sheet11 having release sheets 12 a, 12 b. The photo-curable adhesive sheet 11having release sheet 12 b is placed on an optical information recordingsubstrate 21 having an uneven surface as recording pits and a reflectivelayer 23 (generally reflective layer of Al, Ag or the like having highreflectivity) provided on the uneven surface such that a side having norelease sheet of the photo-curable adhesive sheet 11 faces thereflective layer, and they are depressed. Thus, the side of thephoto-curable adhesive sheet 11 closely adheres to the uneven surface ofthe reflective layer to form a laminate (consisting of 12 b, 11, 23 and21). The release sheet 12 b is removed from the laminate.

Subsequently, another optical information recording substrate 24 havingan uneven surface as recording pits and a reflective layer 25 (orsemitransparent reflective layer) provided on the uneven surface isplaced on an uncured surface (having no substrate), where the releasesheet 12 b is removed, of the photo-curable adhesive sheet 11, such thatthe reflective layer 25 faces the uncured surface of optical informationrecording substrate 24, and they are depressed. Thus, the surface of thephoto-curable adhesive sheet 11 closely adheres to the uneven surface ofthe reflective layer of the substrate to form a laminate (consisting of21, 23, 11, 24 and 25). The photo-curable adhesive sheet 11 of thelaminate is cured by irradiation of ultraviolet rays. Thus the opticalinformation recording medium is obtained.

Otherwise, as shown in FIG. 3, a photo-curable adhesive sheet 11 havingonly a release sheet 12 b is placed on an optical information recordingsubstrate 24 having an uneven surface as recording pits and a reflectivelayer 23 provided on the uneven surface such that a side having norelease sheet of the photo-curable adhesive sheet 11 faces thereflective layer. They are not depressed, and the release sheet 12 b isremoved from the adhesive sheet. Subsequently, another opticalinformation recording substrate 24 is placed on a surface having nosubstrate of the photo-curable adhesive sheet 11, such that thereflective layer 25 faces the surface of the substrate 24, and then theyare depressed at a time. Thus, the surface of the photo-curable adhesivesheet 11 closely adheres to the two uneven surfaces of the reflectivelayers of the substrates to form a laminate. The photo-curable adhesivesheet 11 of the laminate may be cured by irradiation of ultravioletrays.

In the above procedure, a polymer sheet for protection may be bondedonto the adhesive sheet instead of another optical information recordingsubstrate 24. In this case, there is only one uneven surface in thelaminate. Otherwise, a (photo-curable or adhesive) transfer sheet isplaced on an optical information recording substrate having an unevensurface as recording pits and a reflective layer provided on the unevensurface such that the transfer sheet faces the reflective layer.Subsequently, a stamper is depressed on the transfer sheet to form anuneven surface on the transfer sheet (if necessary cured), whereby asubstrate having two uneven surfaces is prepared, and then a polymersheet for protection may be bonded onto the exposed uneven surfacethrough a photo-curable adhesive sheet of the invention.

In the above process, the optical information recording mediumexclusively used for reproduction is explained. However, an opticalinformation recording medium used for recording (writing) is alsoprepared in the same manner as the above process. In the recordablemedium, for example, grooves or grooves and pits is provided instead ofthe pits, and a metal recording layer is provided instead of thereflective or semitransparent reflective layer. When the recording layeris a dye-recording layer, a recording layer and reflective layer aregenerally provided. Besides these points, the recordable medium can bealso prepared in the same manner as above.

The optical information recording substrate may be prepared by aconventional injection molding or by the process comprising depressing astamper on the photo-curable adhesive sheet of the invention, theadhesive sheet or the like. Thus, the optical information recordingsubstrate of the invention can be prepared so as to have a thickness of300 μm or less.

In the process, when the photo-curable adhesive sheet is depressed onthe optical information recording substrate, or when the two opticalinformation recording substrate are superposed on each other through thephoto-curable adhesive sheet such that the reflective layers face eachother, it is preferred to carry out the depressing or superposingoperation under reduced pressure.

The depressing operation under the reduced pressure can be performed bya method comprising passing a substrate and photo-curable adhesive sheetor a substrate, photo-curable adhesive sheet and substrate, between tworolls under reduced pressure; or by a method comprising placing asubstrate in a mold of a vacuum molding device and bring a photo-curableadhesive sheet into contact with the substrate under reduced pressure;or by a method comprising placing a substrate in a mold of a vacuummolding device and bring a photo-curable adhesive sheet and substrateinto contact with the substrate under reduced pressure.

Further, the depressing operation under the reduced pressure can beperformed using a device according to a double vacuum chamber system.The operation is explained by referring to FIG. 4. FIG. 4 shows alaminator according to a double vacuum chamber system. The laminator isprovided with a lower chamber 41, an upper chamber 42, a sheet ofsilicone rubber 43 and a heater 45. A laminate 49 consisting of asubstrate having unevenness and a photo-curable adhesive sheet providedthereon (or laminate of substrate/adhesive sheet/substrate) is placed inthe lower chamber 41 of the laminator. Both the upper chamber 42 andlower chamber 41 are degassed or decompressed. The laminate 49 is heatedwith a heater 45, and air is introduced into the upper chamber 42 toallow the chamber to be at atmospheric pressure while the lower chamber41 is kept under reduced pressure, whereby the laminate is depressed tobe contact bonded. After cooling, the laminate is taken out andtransformed to the next step. This operation permits sufficientdeaeration under reduced pressure, and therefore, the substrate and thephoto-curable adhesive sheet can be contact bonded without bubbles.

The photo-curable adhesive sheet according to the first aspect of theinvention comprises a photo-curable composition which comprises areactive polymer having a photopolymerizable functional group andweight-average molecular weight of not less than 5,000 and which has aglass transition temperature of not more than 20° C.

The photo-curable composition is generally composed mainly of thereactive polymer having a photopolymerizable functional group, acompound (e.g., monomer or oligomer) having a photopolymerizablefunctional group (preferably (meth)acryloyl group), aphotopolymerization initiator and if necessary other additives. Theseare described later.

Subsequently, embodiments according to the second aspect of theinvention are explained in detail by referring to the drawings.

FIG. 5 is a section view showing an example of an embodiment of thephoto-curable transfer sheet 51 used in the present invention. In FIG.5, the photo-curable transfer sheet 51 has release sheets 52 a, 52 b onits both sides. The release sheet may be provided on one side of thephoto-curable transfer sheet, and otherwise may not be provided,depending on uses. Particularly, in a continuous preparation, thephoto-curable transfer sheet 51 having no release sheets is preferred.The photo-curable transfer sheet has the same basic composition as thephoto-curable adhesive sheet of the first aspect.

The photo-curable transfer sheet 51 is a layer that is easily deformedby application of pressure such that it is capable of followingprecisely along an uneven surface of a stamper whereby precisetransferring is brought about when the photo-curable transfer sheet 51is depressed on the uneven surface. The photo-curable transfer sheet 51is mainly composed of a photo-curable composition which comprises areactive polymer having a photopolymerizable functional group andweight-average molecular weight of not less than 5,000, especially thereactive polymer having a glass transition temperature of not more than20° C. Further, the photo-curable transfer sheet 51 has a lighttransmittance of not less than 70% in a wavelength range of 380 to 420nm such that information can be easily read out by a reproduction laserand can recorded in high density. The light transmittance is preferablynot less than 80% in a wavelength range of 380 to 420 nm. Hence, anoptical information recording medium obtained by using the transfersheet can be advantageously used in a process for reproducing pitsignals by using a reproduction laser having a laser wavelength in therange of 380 to 420 nm.

The optical information recording medium can be prepared using the abovephoto-curable transfer sheet, for example, as shown in FIG. 6.

The release sheet 52 a is removed from the photo-curable transfer sheet51 having release sheets 52 a, 52 b (step (1)). The photo-curabletransfer sheet 51 having release sheet 52 b is placed on an opticalinformation recording substrate 61 having an uneven surface as recordingpits and a reflective layer 63 (generally reflective layer of Al, Ag orthe like having high reflectivity) provided on the uneven surface suchthat a side having no release sheet of the photo-curable transfer sheet51 faces the reflective layer, and they are depressed (step (2)). Thus,the side of the photo-curable transfer sheet 51 closely adheres to theuneven surface of the reflective layer to form a laminate (consisting of51, 63 and 61). The release sheet 52 b is removed from the laminate. Ifthis laminate is used in an optical information recording medium, thephoto-curable transfer sheet 51 is cured by ultraviolet rays and thenthe release sheet is removed.

Subsequently, a stamper 64 having an uneven surface as recording pits isplaced on an uncured surface (having no substrate), where the releasesheet 52 b is removed, of the photo-curable transfer sheet 51, such thatthe uneven surface faces the uncured surface of optical informationrecording substrate, and they are depressed (step (3)). Thus, thesurface of the photo-curable transfer sheet 51 closely adheres to theuneven surface of the stamper 64 to form a laminate (consisting of 61,63, 51 and 64). The photo-curable transfer sheet 51 of the laminate isthen cured by irradiation of ultraviolet rays (step (4)), and thestamper is removed from the laminate to form unevenness such asrecording pits on a surface of the cured sheet. Thus the opticalinformation recording medium consisting of the substrate 61, thereflective layer 63 and the cured transfer sheet 51 is obtained. Ingeneral, a silver-alloy reflective layer (semitransparent reflectivelayer) 65 is formed on the unevenness (surface of the cured sheet), andfurther an organic polymer film (cover layer) 66 is bonded onto thesilver-alloy reflective layer 65 through an adhesive layer (step (5)).On the surface of the cured sheet, a photo-curable transfer sheet may befurther depressed, and cured by irradiation of ultraviolet rays.Otherwise, on the surface of the cured sheet, a UV curable resin may befurther coated, and cured.

In the above process, the optical information recording mediumexclusively used for reproduction is explained. However, an opticalinformation recording medium used for recording (writing) is alsoprepared in the same manner as the above process. In the recordablemedium, for example, grooves or grooves and pits is provided instead ofthe pits, and a metal recording layer is provided instead of thereflective or semitransparent reflective layer. When the recording layeris a dye-recording layer, a recording layer and reflective layer aregenerally provided. Besides these points, the recordable medium can bealso prepared in the same manner as above.

In the second aspect according to the invention, the photo-curabletransfer sheet 51 is configured such that the uneven shape of recordedpits of a substrate 61 can be precisely transferred to the photo-curabletransfer sheet 51 by depressing (preferably under reduced pressure) thesheet onto the stamper at low temperature of 100° C. or less (preferablyroom temperature). Superposition of the stamper 61 and the photo-curabletransfer sheet 51 is generally carried out using a pressure rollers oreasy press (preferably under reduced pressure). The photo-curabletransfer sheet 51 after curing is fairly stuck to metal used in thereflective layer, and is not easily peeled from the reflective layer. Ifnecessary, an adhesion-promoting layer may be provided on the reflectivelayer.

In the invention, the photo-curable transfer sheet 51 is configured suchthat the uneven shape of recorded pits of the stamper 64 can beprecisely transferred to photo-curable transfer sheet 51 by depressing(preferably under reduced pressure) the sheet onto the stamper at lowtemperature of 100° C. or less (preferably room temperature).Superposition of the stamper 64 and the photo-curable transfer sheet 51is generally carried out using a pressure rollers or easy press(preferably under reduced pressure). The photo-curable transfer sheet 51after curing is weakly stuck to metal such as nickel used in thestamper, and therefore the photo-curable transfer sheet 51 can be easilypeeled from the stamper 21.

The substrate 61 generally is a thick plate (generally thickness of 0.3to 1.5 mm, especially approx. 1.1 mm), and therefore it can be preparedby conventional injection molding. However, it may be prepared by usingthe photo-curable transfer sheet and a stumper. Since the thickness ofthe optical information recording substrate can be rendered small (300μm or less) by using the photo-curable transfer sheet, another substrateis prepared by conventional injection molding and therefore itsthickness is increased whereby precision of transferred pit shape can beenhanced.

In the process, when the photo-curable transfer sheet is depressed onthe substrate, or when the stamper is depressed on the photo-curableadhesive sheet, it is preferred to carry out the depressing orsuperposing operation under reduced pressure whereby bubbles generatedin the operation can be easily removed.

The depressing operation under the reduced pressure can be performed bya method comprising passing the photo-curable transfer sheet and stamperbetween two rolls under reduced pressure; or by a method comprisingplacing a stamper in a mold of a vacuum molding device and contactbonding a photo-curable transfer sheet to the stamper under reducedpressure.

Further, the depressing operation can be also performed by using thedouble vacuum chamber system shown in FIG. 4, which is used in the firstaspect of the invention. In this case, the depressing operation iscarried out under the condition that a laminate of the substrate havingunevenness and photo-curable transfer sheet or a laminate of thesubstrate, photo-curable transfer sheet and stamper is placed in thelower chamber 41 of the laminator.

The photo-curable transfer sheet used in the second aspect of theinvention preferably comprises a photo-curable composition whichcomprises a reactive polymer having a photopolymerizable functionalgroup and a glass transition temperature of not more than 20° C.

The photo-curable composition is generally composed mainly of thereactive polymer having a photopolymerizable functional group, acompound (e.g., monomer or oligomer) having a photopolymerizablefunctional group (preferably (meth)acryloyl group), aphotopolymerization initiator and if necessary other additives. Thephoto-curable composition used in the second aspect is basically thesame as that of the photo-curable adhesive sheet of the first aspect.

Subsequently, embodiments according to the third aspect of the inventionare explained in detail by referring to the drawings.

FIGS. 8(a) and (b) is a section view showing examples of embodiments ofthe photo-curable transfer sheet 81 used in the present invention. InFIG. 8(a), the photo-curable transfer sheet 81 has a release sheet 82 aon its one side and a release sheet 82 a on the other side. The releasesheet may be provided on one side, and otherwise may not be provided,depending on uses. In FIG. 8(b), the photo-curable transfer sheet 81 hasa release sheet 82 a on its one side and a support 82 c on the otherside.

The photo-curable transfer sheet 81 according to the third aspect has anexcellent smooth surface, and its surface roughness (Ra) is not morethan 30 m, preferably not more than 10 nm. The photo-curable transfersheet 81 having an excellent smooth surface can be obtained, forexample, by casting a melt of a photo-curable composition whichcomprises a reactive polymer having a photopolymerizable functionalgroup and weight-average molecular weight of not less than 5,000 andwhich is capable of deforming by application of pressure on a surface ofa support, the surface having a surface roughness (Ra) of not more than30 nm. Example of the support includes a film made of polycarbonate,which is commercially available. Otherwise, the photo-curable transfersheet 81 can be obtained, for example, by applying a coating liquid ofthe above photo-curable composition onto a surface of the support havinga surface roughness (Ra) of not more than 30 m (especially not more than10 nm), and drying a layer of the coating liquid. However, the formermethod is preferred since it brings about a lower surface roughness.

It is preferred that the photo-curable transfer sheet 81 is mainlycomposed of a photo-curable composition which comprises a reactivepolymer having a photopolymerizable functional group and a glasstransition temperature of not more than 20° C. Further, thephoto-curable transfer sheet has a light transmittance of not less than70% in a wavelength range of 380 to 420 nm such that information can beeasily read out by a reproduction laser. The light transmittance ispreferably not less than 80% in a wavelength range of 380 to 420 nm.Hence, an optical information recording medium obtained by using thetransfer sheet can be advantageously used in a process for reproducingpit signals by using a reproduction laser having a laser wavelength inthe range of 380 to 420 nm.

The optical information recording substrate and laminate can be preparedusing the above photo-curable transfer sheet 81, for example, as shownin FIG. 9.

When the photo-curable transfer sheet 81 having release sheets 82 a, 82a on both sides is used, the preparation is carried out below. Therelease sheet 82 b is removed from the photo-curable transfer sheet 81,and the transfer sheet is disposed on an uneven surface of a stamper 91having the uneven surface of recorded pits such that a surface having norelease sheet of the photo-curable transfer sheet 81 faces the unevensurface, and they are superposed and depressed such that thephoto-curable transfer sheet 81 is brought into close contact with theuneven surface, whereby a laminate having the stamper 91 and thephoto-curable transfer sheet 81 is obtained. Then, the release sheet 82a of the photo-curable transfer sheet 81 is exposed to UV (ultravioletrays), whereby the photo-curable transfer sheet 81 is cured and then thestamper 91 and the release sheet 82 a are removed from the laminate toobtain the cured photo-curable transfer sheet 81 having unevenness(i.e., optical information recording substrate) 90. The surface havingno unevenness of this substrate has a surface roughness (Ra) is not morethan 30 nm, preferably not more than 10 nm.

In case the photo-curable transfer sheet 81 having a release sheet 82 aon its one side and a support 82 c on the other side is used, theresultant substrate has a smooth surface of the support and both smoothsurfaces in the interface between the support and transfer sheet, thesesurfaces having a surface roughness (Ra) is not more than 30 nm,preferably not more than 10 nm.

In the invention, the photo-curable transfer sheet is configured suchthat the uneven shape of recorded pits of the stamper 91 can beprecisely transferred to the photo-curable transfer sheet by depressingthe sheet onto the stamper at low temperature of 100° C. or less.Superposition of the stamper 91 and the photo-curable transfer sheet 81is generally carried out using a pressure rollers or easy press,preferably under reduced pressure. The photo-curable transfer sheet 81after curing is weakly stuck to metal such as nickel used in thestamper, and therefore the photo-curable transfer sheet 81 can be easilypeeled from the stamper 91.

The optical information recording medium can be prepared using theabove-mentioned optical information recording substrate 90, for example,as shown in FIG. 10.

The uneven surface of the optical information recording substrate 90obtained above is metallized (deposited) by sputtering process usingsilver alloy, whereby a silver-alloy reflective layer (semitransparentreflective layer) 83 is formed on the substrate. Separately, the unevensurface of an optical information recording substrate 100 is metallizedby sputtering process using aluminum, whereby an Al reflective layer 103(or silver-alloy reflective layer having higher reflectivity than thelayer 83) is formed on the substrate. The substrate 90 having thesemitransparent reflective layer 83 and the substrate 100 having the Alreflective layer 103 are disposed such that both the reflective layersface each other and superposed through an adhesive, and the adhesive iscured to form an adhesive layer 104, whereby the optical informationrecording medium 110 is obtained. The surface having no unevenness ofthe sheet 11 of this optical information recording medium 110 has asurface roughness (Ra) of not more than 30 nm (especially not more than10 nm). Since reading of signals is carried out by exposing areproduction light (laser) to the surface, there are little errors inreading. On this surface, further a support or a protective film may beprovided.

In the above process, the optical information recording mediumexclusively used for reproduction is explained. On the other hand, inthe recordable medium, for example, grooves or grooves and pits isprovided instead of the pits, and a metal recording layer is providedinstead of the reflective layer or semitransparent reflective layer.When the recording layer is a dye-recording layer, a recording layer andreflective layer are provided. Besides the points, the recordable mediumis prepared in the same manner as the above process.

The optical information recording substrate 100, which is generally athick plate, may be prepared by a conventional injection molding or bythe process for the preparation of the optical information recordingsubstrate as mentioned previously. The optical information recordingsubstrate can be prepared so as to have a thickness of 300 μm or less,and therefore, when another substrate is prepared by a conventionalprocess, the thickness of the another substrate can be increased toenhance the precision of pit and/or groove shape. The adhesives used forforming the adhesive layer include a conventional hot-melt typeadhesive, a UV-curable resin adhesive and a pressure-sensitive contactadhesive.

Further, the following media are preferred: Two optical informationrecording substrates 90 mentioned above, i.e., one substrate having afull reflective layer such as Al layer and the other substrate having asemitransparent reflective layer, are prepared, the two substrates arebonded to each other through an adhesive such that the semitransparentreflective layer faces the surface having no unevenness to form alaminate, and another laminate is prepared in the same manner as above,the resultant two laminates are bonded to each other through an adhesivesuch that both the reflective layers face each other, and hence anoptical information recording medium having four recorded surfaces isobtained. Further, the above one laminate is bonded onto a transparentsupporting substrate whereby an optical information recording mediumshown in FIG. 11 can be obtained. Furthermore, the above one laminate isbonded onto a conventional transparent supporting substrate havinguneven surface and a reflective layer thereon to give an opticalinformation recording medium. In these media, the semitransparentreflective layer is provided on the incident side of the reading laserbeam.

These media can be used as conventional four-layer type and three-layertype in double sides reading system and two-layer type in single sidereading system, respectively.

Otherwise, unevenness is formed on a part of a substrate, a reflectivelayer is formed thereon, and a recording layer, on which information canbe written, may be provided thereon.

Based on the process explained above by referring to FIGS. 9 and 10,another procedure to obtain the optical information recording mediumhaving the specific surface roughness is described below. The procedureis carried out by using a photo-curable transfer sheet having no smoothsurface instead of the transfer sheet having the specific surfaceroughness and, after preparation of a laminate, giving surfacesmoothness to the resultant laminate. This procedure can be also appliedto the case that the transfer sheet of the medium has insufficientlysmooth surface, which results from treatments during the preparation ofmedium even if a release sheet having excellent smooth surface is used,or from the use of a release sheet having poor smooth surface.

In FIG. 9, after the preparation of the optical information recordingsubstrate 90 (i.e., cured photo-curable transfer sheet having unevenness81), a coating liquid of ultraviolet curable resin is applied onto thereverse surface having no unevenness of the substrate by a spin coateror a screen printing method and the resultant coating liquid layer isexposed to ultraviolet rays for curing the layer, in order to enhancesmoothness of the surface. The coating liquid of an ultraviolet curableresin mainly comprises compounds having a photopolymerizable functionalgroup(s) and a photopolymerization initiator as described later, andfurther a surfactant such as a leveling agent and if desired an organicsolvent. Further, in order to enhance the smoothness of the surface, inaddition to the surfactant such as a leveling agent, polymers describedlater may be added to the coating liquid. Besides the above additives,the coating liquid may contain a UV light absorber, an aging resistantagent, a dye and/or a processing auxiliary. If necessary, the coatingliquid may contain a particle of material such as silica gel, calciumcarbonate or silicone copolymer in a small amount. It is generallypreferred to use an ultraviolet curable resin for forming hard coatlayer, which has excellent leveling prosperity and also can give highhardness.

The conditions for application of the coating liquid generally includeviscosity of the coating liquid in the range of 10 to 1,000 [mPas/25°C.], the setting time in the range of 1 to 100 sec., the exposing timein the range of 1 to 20 sec., and the thickness in the range of 1 to 10μm.

The application of the coating liquid can be carried out in anappropriate step in the process shown in FIG. 10. For example, theapplication can be carried out after metal is sputtered, or after themedium is finished.

In the process, when the photo-curable transfer sheet is depressed onthe stamper, or when the two optical information recording substratesare superposed on each other through adhesive such that the reflectivelayers face each other, it is preferred to carry out the depressing orsuperposing operation under reduced pressure whereby bubbles generatedin the operation can be smoothly moved.

The depressing operation under the reduced pressure can be performed bya method comprising passing the photo-curable transfer sheet and stamperbetween two rolls under reduced pressure; or by a method comprisingplacing a stamper in a mold of a vacuum molding device and contactbonding a photo-curable transfer sheet to the stamper under reducedpressure.

Further, the depressing operation can be also performed by using thedouble vacuum chamber system shown in FIG. 4, which is used in the firstaspect of the invention. In this case, the depressing operation iscarried out under the condition that a laminate the substrate,photo-curable transfer sheet and stamper, or a laminate of thesubstrate, adhesive and substrate (the substrates having unevenness) isplaced in the lower chamber 41 of the laminator.

The photo-curable transfer sheet according to the third aspect of theinvention preferably consists mainly of a photo-curable compositionwhich comprises a reactive polymer having a photopolymerizablefunctional group and weight-average molecular weight of not less than5,000 and especially which has a glass transition temperature of notmore than 20° C. The transfer sheet has the same construction as that ofthe second aspect expect that it has a smooth surface.

The photo-curable composition of the invention is generally composedmainly of the reactive polymer having a photopolymerizable functionalgroup, a compound (e.g., monomer or oligomer) having aphotopolymerizable functional group (preferably (meth)acryloyl group), aphotopolymerization initiator, and if necessary other additives.

Examples of the reactive polymer having a photopolymerizable functionalgroup include homopolymers or copolymers (i.e., acrylic resins having aphotopolymerizable functional group) derived from alkyl acrylate (e.g.,methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate)and/or alkyl methacrylate (e.g., methyl methacrylate, ethylmethacrylate, butyl methacrylate, 2-ethylhexyl methacrylate) and havinga photopolymerizable functional group on its main chain or side chain.These (co)polymers can be obtained, for example, by copolymerizing oneor more (meth)acrylate mentioned above with (meth)acrylate (e.g.,2-hydroxyethyl (meth)acrylate) having a functional group such as —OH andreacting the resultant polymer with a compound (e.g., isocyanatoalkyl(meth)acrylate) having a functional group capable of reacting with thefunctional group of the polymer and having a photopolymerizablefunctional group. Thus an acrylic resin having a photopolymerizablefunctional group through a urethane bond is preferred.

The reactive polymer of the invention has generally 1 to 50% by mole,preferably 5 to 30% by mole of the photopolymerizable functional group.Examples of the photopolymerizable functional group preferably includeacryloyl, methacryloyl and vinyl groups, especially acryloyl andmethacryloyl groups.

In case the reactive polymer having glass transition temperature of notmore than 20° C. is used as above, the resultant photo-curable sheethaving flexibility can follow exactly the uneven surface of the stampereven at room temperature when the sheet is depressed on the stamper. Thereactive polymer especially has glass transition temperature of 15 to−50° C. because the resultant photo-curable layer can follow moreexactly the uneven surface. When the glass transition temperatureexceeds the upper limit, high pressure and temperature is needed in thedepressing and bonding steps of the sheet, which brings about loweringof workability. When the glass transition temperature falls to below thelower limit, the resultant cured sheet does not have sufficienthardness.

The reactive polymer of the invention generally has number-averagemolecular weight of 5,000 to 1,000,000, preferably 10,000 to 300,000,and/or generally has weight-average molecular weight of 5,000 to1,000,000, preferably 10,000 to 300,000.

Examples of the compounds having a photopolymerizable group include(meth)acrylate monomers such as 2-hydroxyethyl(meth)acrylate,2-hydroxyropyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate,2-ethylhexylpolyethoxy(meth)acrylate, benzyl(meth)acrylate,isobornyl(meth)acrylate, phenyloxyethyl(meth)acrylate, tricyclodecanemono(meth)acrylate, dicyclopentenyloxyethyl(meth)acrylate,tetrahydrofurfuryl(meth)acrylate, acryloylmorpholine,N-vinylcaprolactam, 2-hydroxy-3-phenyloxypropyl(meth)acrylate,o-phenylphenyloxyethyl(meth)acrylate, neopentylglycol di(meth)acrylate,neopentyl glycol dipropoxydi(meth)acrylate, neopentyl glycolhydroxypivalate di(meth)acrylate, tricyclodecanedimethyloldi(meth)acrylate, 1,6-hexanediol di(meth)acrylate, nonanedioldi(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritoltri(meth)acrylate, pentaerythritol tetra(meth)acrylate,tris[(meth)acryloxyethyl]isocyanurate and ditrimethylolpropanetetra(meth)acrylate; and

-   -   the following (meth)acrylate oligomer such as:    -   polyurethane (meth)acrylate such as compounds obtained by        reaction of:    -   a polyol compound (e.g., polyol such as ethylene glycol,        propylene glycol, neopentyl glycol, 1,6-hexanediol,        3-methyl-1,5-pentanediol, 1,9-nonanediol,        2-ethyl-2-butyl-1,3-propanediol, trimethylolpropane, diethylene        glycol, dipropylene glycol, polypropylene glycol,        1,4-dimethylolcyclohexane, bisphenol-A polyethoxydiol and        polytetramethylene glycol; polyesterpolyol obtained by reaction        of the above-mentioned polyol and polybasic acid or anhydride        thereof such as succinic acid, maleic acid, itaconic acid,        adipic acid, hydrogenated dimer acid, phthalic acid, isophthalic        acid and terephthalic acid; polycaprolactone polyol obtained by        reaction of the above-mentioned polyol and ε-caprolactone; a        compound obtained by reaction of the above-mentioned polyol and        a reaction product of the above-mentioned polybasic acid or        anhydride thereof and ε-caprolactone; polycarbonate polyol; or        polymer polyol), and    -   an organic polyisocyanate compound (e.g., tolylene diisocyanate,        isophorone diisocyanate, xylylene diisocyanate,        diphenylmethane-4,4′-diisocyanate, dicyclopentanyl diisocyanate,        hexamethylene diisocyanate, 2,4,4′-trimethylhexamethylene        diisocyanate, 2,2′,4′-trimethylhexamethylene diisocyanate), and    -   hydroxyl-containing (meth)acrylate (e.g., 2-hydroxyethyl        (meth)acrylate, 2-hydroxyropyl (meth)acrylate, 4-hydroxybutyl        (meth)acrylate, 2-hydroxy-3-phenyloxypropyl (meth)acrylate,        cyclohexane-1,4-dimethylolmono(meth)acrylate, pentaerythritol        tri(meth)acrylate or glycerol di(meth)acrylate);    -   bisphenol-type epoxy(meth)acrylate obtained by reaction of        bisphenol-A epoxy resin or bisphenol-F epoxy resin and        (meth)acrylic acid.

These compounds having photopolymerizable functional group can beemployed singly or in combination of two or more kinds.

Any photopolymerization initiators known can be used in the invention.The initiators having good storage-stability after mixing with othercomponents are preferred. Examples of the photopolymerization initiatorsinclude acetophenone type initiators such as2-hidroxy-2-methyl-1-phenylpropane-1-on, 1-hydroxycyclohexylphenylketoneand 2-methyl-1-[4-(methylthio)phenyl]-2-morphorino-propane-1-on; benzointype initiators such as benzylmethylketal; benzophenone type initiatorssuch as benzophenone, 4-phenylbenzophenone and hydroxybenzophenone;thioxanthone type initiators such as isopropylthioxanthone and2,4-diethythioxanthone. Further, as special type, there can be mentionedmethylphenylglyoxylate. Especially preferred are2-hidroxy-2-methyl-1-phenylpropane-1-on,1-hydroxycyclohexylphenylketone,2-methyl-1-[4-(methylthio)phenyl]-2-morphorino-propane-1-on andbenzophenone. These photopolymerization initiators can be employedtogether with one or more kinds of a photopolymerization promoter suchas a benzoic acid type compound (e.g., 4-dimethylaminobezoic acid) or atertiary amine compound by mixing the initiator with the promoter inoptional ratio. Only the initiator can be employed singly or incombination of two or more kinds. The initiator is preferably containedin the photo-curable composition in the range of 0.1 to 20% by weight,particularly 1 to 10% by weight.

In addition to the above-mentioned photopolymerizable initiators, theacetophenone type initiator includes 4-phenoxydichloroacetophenone,4-t-butyldichloroacetophenone, 4-t-butyltrichloroacetophenone,diethoxyacetophenone, 2-hidroxy-2-methyl-1-phenylpropane-1-on,1-(4-isopropylphenyl)-2-hidroxy-2-methylpropane-1-on,1-(4-dodecylphenyl)-2-hydroxy-2-methylpropane-1-on,4-(2-hydroxyethoxy)-phenyl(2-hydroxy-2-propyl)ketone,1-hydroxycyclohexylphenylketone,2-methyl-1-[4-(methylthio)phenyl]-2-morphorino-propane-1-on; and thebenzophenone type initiators include benzophenone, benzoylbenzoic acid,methyl benzoylbenzoate, 4-phenylbenzophenone, hydroxybenzophenone,4-benzoyl-4′-methylphenylsulfide and3,3′-dimethyl-4-methoxybenzophenone.

The acetophenone type initiators preferably are2-hidroxy-2-methyl-1-phenylpropane-1-on,1-hydroxycyclohexylphenylketone,2-methyl-1-[4-(methylthio)phenyl]-2-morphorino-propane-1-on, and thebenzophenone type initiators preferably are benzophenone, benzoylbenzoicacid and methyl benzoylbenzoate.

Preferred examples of the tertiary amine compounds of thephotopolymerization promoter include triethanolamine,methyldiethanolamine, triisopropanolamine,4,4′-dimethylaminobenzophenone, 4,4′-diethylaminobenzophenone, ethyl2-dimethylaminobenzonate, ethyl 4-dimethylaminobenzonate,(n-butoxy)ethyl 4-dimethylaminobenzonate, isoamyl4-dimethylaminobenzonate and 2-ethylhexyl 4-dimethylaminobenzonate.Especially preferred are ethyl 4-dimethylaminobenzonate, (n-butoxy)ethyl4-dimethylaminobenzonate, isoamyl 4-dimethylaminobenzonate and2-ethylhexyl 4-dimethylaminobenzonate.

The photo-curable composition of the invention is preferably configuredsuch that the photo-curable (adhesive or transfer) sheet has a glasstransition temperature of not more than 20° C. and the photo-curable(adhesive or transfer) sheet before and after curing has a transmittanceof not less than 70%. Therefore the photo-curable composition preferablycontains, in addition to the compound having a photopolymerizablefunctional group and the photopolymerization initiator, if desired thefollowing thermoplastic resin and other additives.

The ratio by weight of the reactive polymer: the compound having aphotopolymerizable functional group: the photopolymerization initiatorgenerally is 40-100:0-60:0.1-10, preferably 60-100:0-40:1-10, especially50-80:20-50:1-10.

As other additives, a silane coupling agent can be used for enhancingthe adhesive strength. Examples of the silane coupling agent includevinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane,γ-methacryloxypropylmethoxysilane, vinyltriacetoxysilane,γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane,β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,γ-chloropropylmethoxysilane, vinyltrichlorosilane,γ-mercaptopropylmethoxysilane, γ-aminopropyltriethoxysilane,N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane. The silane couplingagent can be used singly, or in combination of two or more kinds. Thesilane coupling agent is preferably used in the range of 0.01 to 5weight by part based on 100 parts by weight of the above reactivepolymer.

Similarly, an epoxy group-containing compound can be used for enhancingthe adhesive strength. Examples of the epoxy group-containing compoundsinclude triglycidyl tris(2-hydroxyethyl)isocyanurate, neopentylglycoldiglycidyl ether, 1,6-hexanediol diglycidyl ether, allyl glycidyl ether,2-ethylhexyl glycidyl ether, phenyl glycidyl ether, phenol glycidylether, p-tert-butylphenyl glycidyl ether, diglycidyl adipate, diglycidylo-phthalate, glycidyl methacrylate and butyl glycidyl ether. Further,the similar effect is also obtained by using an oligomer having an epoxygroup and molecular weight of hundreds to thousands, or a polymer havingan epoxy group and molecular weight of thousands to hundreds ofthousands. The content of the compound having an epoxy group issufficient in the range of 0.1 to 20 parts by weight based on 100 partsby weight of the reactive polymer, particularly 1 to 10% by weight. Atleast one of the compounds having an epoxy group can be used singly orin combination of two or more kinds.

As other additives, further a hydrocarbon resin can be used forimproving processing properties such as laminating properties. Thehydrocarbon resin may be either natural resin or synthetic resin.Examples of the natural resins preferably include rosins, rosinderivatives and terpene resins. Examples of the rosins include gumresins, tall oil resins, wood resins. Examples of the rosin derivativesinclude hydrogenated rosins, disproportionated rosins, polymerizedrosins, esterificated rosins, metal salts of rosins. Examples of theterpene resins include α-pinene resins, β-pinene resins, and terpenephenol resins. Moreover, as the natural resin, dammar, copal, shellaccan be used. Examples of the synthetic resins preferably includepetroleum resins, phenol resins, and xylene resins. Examples of thepetroleum resins include aliphatic petroleum resins, aromatic petroleumresins, cycoaliphatic petroleum resins, copolymer type petroleum resins,hydrogenated petroleum resins, pure monomer type petroleum resins, andcoumarone-indene resins. Examples of the phenol resins includealkylphenol resins and modified phenol resins. Examples of the xyleneresins include xylene resins and modified xylene resins.

Furthermore, acrylic resin can be employed in the invention. Forexample, homopolymers and copolymers obtained from alkyl acrylate(s)such as methyl acrylate, ethyl acrylate and butyl acrylate and/or alkylmethacrylate(s) such as methyl methacrylate, ethyl methacrylate andbutyl methacrylate can be used. Copolymers of these monomers and othercopolymerizable monomers can be also used. In view of reactivity in thephoto curing step and durability and transparency of cured product,polymethyl methacrylate (PMMA) is preferred.

The above-mentioned polymer such as hydrocarbon resin can be used in theamount of 1 to 20 parts by weight, preferably 5 to 15 parts by weightbased on 100 parts by weight of the reactive polymer.

The photo-curable composition may contain, in addition to theabove-mentioned additives, an ultraviolet absorber, an aging resistantagent, a dye, and a processing auxiliary agent in a small amount. Ifdesired, particles of silica gel, calcium carbonate or siliconecopolymer may be contained in a small amount.

The photo-curable adhesive or transfer sheet comprising thephoto-curable composition of the invention is generally prepared byhomogeneously mixing the reactive polymer, a compound having aphotopolymerizable functional group (monomer and oligomer) and ifdesired other additives, kneading the mixture using an extruder or roll,and subjecting the kneaded mixture to a film-forming process using acalendar, roll, T-die extrusion or inflation to form a film of apredetermined dimension. When a support is used, it is needed to form afilm on the support. A more preferred process for forming thephoto-curable sheet comprises the steps of: dissolving homogeneously thecomponents in a good solvent, applying the resultant solution onto aseparator coated closely with silicone or fluoric resin (or the support)by means of flow-coater method, roll-coater method, gravure-roll method,mayer-bar method or lip-die coating method, and vaporizing the solvent.

The surface of the photo-curable sheet may be embossed in the filmformation process to prevent blocking and facilitate deaeration in thestep depressing the sheet and the substrate or stamper. As methods forthe embossing processing, conventional methods such as a method usingembossing roll can be adopted. In a process for applying a solution, itis possible that the solution is applied onto an embossed film or paperhaving release properties whose emboss shape is transferred to thesheet. Mean surface roughness (Ra) of the embossed surface is generallynot more than 50 μm, preferably 0.01 to 50 μm, especially 0.1 to 20 μm,whereby air is easily escaped from an interface between the sheet and adevice to permit the embossed surface of the sheet to fill upcomplicated unevenness of the device. The mean surface roughness of lessthan 0.01 μm is apt to bring about poor deaeration, whereas the meansurface roughness of more than 50 μm occasionally allows the unevennessof the sheet to remain in the depressing step.

The thickness of the photo-curable adhesive or transfer layer generallyis in the range of 1 to 1,200 μm, preferably 5 to 500 μm, especially 5to 300 μm. When the thickness is thinner than 1 μm, sealing propertiesare lowered and maybe the sheet does not full up the unevenness of thetransparent substrate. When the thickness is thicker than 1,200 μm, thethickness of the resultant recording medium is so thick whereby troublein housing or storing of the medium and the resultant assembly orreverse influence in light transmittance possibly occurs.

The release sheet preferably comprises transparent organic resin havinga glass transition temperature of not less than 50° C. The release sheetgenerally is a transparent resin sheet mainly consisting of organicresin such as polyester resin (e.g., polyethylene terephthalate,polycyclohexylene terephthalate, polyethylene naphthalate), polyamide(e.g., nylon 46, modified nylon 6T, nylon MXD6, polyphthalamide), ketoneresin (e.g., polyphenylene sulfide, polythioether sulfone), sulfoneresin (e.g., polysulfone, polyether sulfone), polyether nitrile,polyarylate, polyether imide, polyamideimide, polycarbonate, polymethylmethacrylate, triacetylcellulose, polystyrene or polyvinyl chloride. Ofthese resins, polycarbonate, polymethyl methacrylate, polyvinylchloride, polystyrene and polyethylene terephthalate can be preferablyemployed. The thickness is generally in the range of 10 to 200 μm,especially in the range of 30 to 100 μm.

The photo-curable transfer sheet having a smooth surface according tothe third aspect can be, for example, obtained by extruding the kneadedmixture as mentioned above to cast and cool a sheet having a surfaceroughness (Ra) of not more than 30 nm. If necessary, the other surfacemay be covered by a sheet (release sheet). Otherwise, the photo-curabletransfer sheet can be, for example, obtained by dissolving homogeneouslythe components in a good solvent, applying the resultant solution onto aseparator coated closely with silicone or fluoric resin (support) bymeans of flow-coater method, roll-coater method, gravure-roll method,mayer-bar method or lip-die coating method, and vaporizing the solvent.Particularly, the photo-curable transfer sheet having a smooth surfacecan be obtained by applying the resultant solution onto a support(preferably polycarbonate sheet) having a surface roughness of not morethan 30 nm, and drying the solution layer.

The thickness of the photo-curable transfer sheet of the third aspect isin the range of 1 to 1,200 μm, preferably 5 to 500 μm, especially 5 to300 μm (particularly not more than 150 μm). When the thickness isthinner than 1 μm, sealing properties are lowered and maybe the sheetdoes not full up the unevenness of the transparent substrate. When thethickness is thicker than 1,200 μm, the thickness of the resultantrecording medium is so thick whereby trouble in housing or storing ofthe medium and the resultant assembly or reverse influence in lighttransmittance possibly occurs.

The support of the third aspect preferably comprises transparent organicresin having a glass transition temperature of not less than 50° C. Thesupport generally is a transparent resin sheet mainly consisting oforganic resin such as polyester resin (e.g., polyethylene terephthalate,polycyclohexylene terephthalate, polyethylene naphthalate), polyamide(e.g., nylon 46, modified nylon 6T, nylon MXD6, polyphthalamide), ketoneresin (e.g., polyphenylene sulfide, polythioether sulfone), sulfoneresin (e.g., polysulfone, polyether sulfone), polyether nitrile,polyarylate, polyether imide, polyamideimide, polycarbonate, polymethylmethacrylate, triacetylcellulose, polystyrene or polyvinyl chloride. Ofthese resins, polycarbonate, polymethyl methacrylate, polyvinylchloride, polystyrene and polyethylene terephthalate are excellent intransparency and birefringence, and therefore can be preferablyemployed.

The release sheet having surface roughness (Ra) of not more than 30 nmaccording to the third aspect preferably comprises transparent organicresin having a glass transition temperature of not less than 50° C. Therelease sheet generally is a transparent resin sheet mainly consistingof organic resin such as polyester resin (e.g., polyethyleneterephthalate, polycyclohexylene terephthalate, polyethylenenaphthalate), polyamide (e.g., nylon 46, modified nylon 6T, nylon MXD6,polyphthalamide), ketone resin (e.g., polyphenylene sulfide,polythioether sulfone), sulfone resin (e.g., polysulfone, polyethersulfone), polyether nitrile, polyarylate, polyether imide,polyamideimide, polycarbonate, polymethyl methacrylate,triacetylcellulose, polystyrene or polyvinyl chloride. Of these resins,polycarbonate, polymethyl methacrylate, polyvinyl chloride, polystyreneand polyethylene terephthalate are excellent in transparency, andtherefore can be preferably employed.

The substrate having uneven surface used in the invention preferablycomprises transparent organic resin having a glass transitiontemperature of not less than 50° C. The substrate generally is atransparent resin sheet mainly consisting of organic resin such aspolyester resin (e.g., polyethylene terephthalate, polycyclohexyleneterephthalate, polyethylene naphthalate), polyamide (e.g., nylon 46,modified nylon 6T, nylon MXD6, polyphthalamide), ketone resin (e.g.,polyphenylene sulfide, polythioether sulfone), sulfone resin (e.g.,polysulfone, polyether sulfone), polyether nitrile, polyarylate,polyether imide, polyamideimide, polycarbonate, polymethyl methacrylate,triacetylcellulose, polystyrene or polyvinyl chloride. Of these resins,polycarbonate, polymethyl methacrylate, polyvinyl chloride, polystyreneand polyethylene terephthalate are excellent in transferring properties,transparency and birefringence, and therefore can be preferablyemployed. The thickness is generally in the range of 200 to 2,000 μm,especially in the range of 50 to 1,500 μm.

The polymer film for protection used in the invention preferablycomprises transparent organic resin having a glass transitiontemperature of not less than 50° C. The film generally is a transparentresin sheet mainly consisting of organic resin such as polyester resin(e.g., polyethylene terephthalate, polycyclohexylene terephthalate,polyethylene naphthalate), polyamide (e.g., nylon 46, modified nylon 6T,nylon MXD6, polyphthalamide), ketone resin (e.g., polyphenylene sulfide,polythioether sulfone), sulfone resin (e.g., polysulfone, polyethersulfone), polyether nitrile, polyarylate, polyether imide,polyamideimide, polycarbonate, polymethyl methacrylate,triacetylcellulose, polystyrene or polyvinyl chloride. Of these resins,polycarbonate, polymethyl methacrylate, polyvinyl chloride, polystyreneand polyethylene terephthalate are excellent in transparency andbirefringence, and therefore can be preferably employed. The thicknessis generally in the range of 10 to 200 μm, especially in the range of 50to 100 μm.

The photo-curable adhesive or transfer sheet of the invention obtainedas above generally comprises the photo-curable composition containingthe reactive polymer of a glass transition temperature of not more than20° C. Further, the photo-curable adhesive or transfer sheet (generallycorresponding to optical information recording substrate) generally hasa light transmittance of not less than 70% in a wavelength rang of 380to 420 nm, preferably 380 to 800 nm. In more detail, by setting theglass transition temperature of the reactive polymer to not more than20° C., the resultant photo-curable sheet having flexibility can followexactly the uneven surface of the stamper even at room temperature whenthe sheet is depressed on the stamper. Especially, in the case of theglass transition temperature of 15 to −50° C., the properties followingexactly the uneven surface of the stamper is further improved. When theglass transition temperature is so high, high pressure and temperatureis needed in the depressing or bonding operation whereby the workabilityis reduced. When the glass transition temperature is so low, theresultant sheet after curing does not have sufficient hardness.

As described above, the (cured) photo-curable adhesive or transfer sheetgenerally has a light transmittance of not less than 70% in a wavelengthrang of 380 to 420 nm, preferably 380 to 800 nm, whereby reduction ofthe strength of signals to be read out with a laser beam can beprevented. Further, the sheet preferably has a light transmittance ofnot less than 80% in a wavelength rang of 380 to 420 nm.

The reactive polymer of the photo-curable composition preferably has 1to 50% by mole of polymerizable functional group, whereby the curedphoto-curable sheet has strength capable of holding its shape. Thephotopolymerization initiator is preferably used in the amount of 0.1 to10% by weight as described previously. The amount of less than the lowerlimit causes workability to reduce owing to slow curing rate, whereasthe amount of more than the upper limit causes the properties followingexactly the uneven or rough surface of the stamper to reduce.

The photo-curable adhesive or transfer sheet of the invention can beoffered as a film precisely controlled in the thickness, and thereforeit is possible to easily and precisely bond the sheet to the unevensurface such as the substrate or stamper. This bonding (contact bonding)can be easily carried out by depressing the sheet and stamper by meansof easy method using pressure rollers or easy press to temporarily bondthem at temperature of 20 to 100° C., and then curing the sheet byexposing it to light at room temperature for one to tens seconds.Further, the temporarily bonded laminate is free from occurrence ofslippage or peeling between of the sheet and stamper or substrate owingto its specific adhesion, and hence the laminate can be freely handleduntil the light-curing step.

In case the photo-curable adhesive or transfer sheet of the invention iscured, it is possible to adopt, as light source used, various sourcesgenerating light in the wavelength range of ultraviolet to visible rays.Examples of the sources include super-high-pressure, high-pressure andlow-pressure mercury lamps, a chemical lamp, a xenon lamp, a halogenlamp, a mercury halogen lamp, a carbon arc lamp, and an incandescentelectric lamp, and laser beam. The exposing time is generally in therange of a few seconds to a few minutes, depending upon kinds of thelamp and strength of light. To promote the curing, the laminate may beheated beforehand for 30 to 80° C., and then the heated laminate may beexposed to ultraviolet rays.

The metal reflective layer of the invention is formed on an unevensurface of the resultant cured photo-curable sheet having the unevensurface by metallizing (e.g., spattering, vacuum deposition,ion-plating). Examples of the metal materials include aluminum, gold,silver or alloy thereof. The semitransparent reflective layer providedon the sheet is generally formed by using silver as metal. In moredetail, the semitransparent reflective layer is required to have lowreflectivity compared with the reflective layer, and therefore is formedby changing the materials and/or the thickness.

When the organic polymer film is bonded onto the reflective layer of thecured sheet, an adhesive is applied onto one of the film and the sheet,and the other is superposed on the adhesive layer, which is cured. Whenthe adhesive is UV-curable resin, it is cured by UV irradiation, andwhen the adhesive is hot-melt type, it is applied to the reflectivelayer under heating and then cooled.

In the preparation of the optical information recording medium of theinvention, it is continuously processed in the form of sheet and finallypunched out in the form of disc. However, it may be processed in theform of disc before the bonding.

EXAMPLE

The invention is illustrated in detail using the following Examples.

Example 1

<Preparation of Photo-Curable Adhesive Sheet>

(Preparation of Reactive Polymer) Formulation I 2-ethylhexylmethacrylate 70 parts by weight methyl methacrylate 20 parts by weight2-hydroxyethyl methacrylate 10 parts by weight benzophenone 5 parts byweight toluene 30 parts by weight ethyl acetate 30 parts by weight

A mixture of the above Formulation I was heated to 60° C. withmoderately stirring to initiate the polymerization, and stirred at thistemperature for 10 hours to provide acrylic resin having a hydroxylgroup on its side chain. Then, 5 parts by weight of Calens MOI(2-isocyanatoethyl methacrylate; available from Showa Denko K.K.) wasadded to the solution of the acrylic resin, and reacted with each otherat 50° C. with moderately stirring to provide a solution 1 containing areactive polymer having a photopolymerizable functional group.

The resultant reactive polymer has Tg of 0° C., weight-average molecularweight of 150,000 and 5% by mole of methacryloyl group on its side.Formulation II solution 1 of reactive polymer 100 parts by weighttricyclodecane diacrylate 30 parts by weight 1-hydroxycyclohexyl phenylketone 1 part by weight

The above Formulation II was homogeneously dissolved to give a mixture,which was applied onto a release sheet (thickness: 75 μm; trade name:No. 23, available from Fujimori Kogyo) and dried to form a photo-curableadhesive sheet (layer) of thickness of 25±2 μm. Thus, the resultantphoto-curable adhesive sheet had the release sheet and therefore thetotal thickness was 100±2 μm.

Preparation of One Optical Information Recording Substrate havingReflective Layer

A photo-curable transfer sheet was prepared in the same manner as in thephoto-curable adhesive sheet. The resultant photo-curable transfer sheethaving release sheet had thickness of 100 μm, which is thicker than theadhesive sheet.

The photo-curable transfer sheet was depressed on an unevenness surfaceof a stamper having the uneven surface as pits using a roller made ofsilicone rubber under load of 2 kg to form a laminate in which the shapeof the uneven surface was transferred to a surface of the photo-curabletransfer sheet.

Subsequently, the photo-curable transfer sheet of the laminate wasexposed to UV-rays of a metal-halide lamp under the condition of anintegrated amount of light of 1,000 mJ/cm² and as a result, thetransferred layer (photo-curable sheet) was cured.

The stamper was peeled from the laminate. Silver alloy was spattered onthe uneven surface of the cured photo-curable layer (optical informationrecording substrate) to form a semitransparent reflective layer ofsilver alloy. Thus, an optical information recording substrate havingreflective layer was prepared.

Preparation of the Other Optical Information Recording Substrate havingReflective Layer

Melt carbonate was poured into a mold having an uneven surface as pitsand solidified to form an optical information recording substrate havingthickness of 1,100 μm. Aluminum was spattered on the uneven surface ofthe optical information recording substrate to form a reflective layerof Al. Thus, the other optical information recording substrate havingreflective layer was prepared.

Preparation of Optical Information Recording Medium

The two optical information recording substrates prepared above werebonded to each other through the photo-curable adhesive sheet preparedabove such that the two reflective layers faced each other to give alaminate, and the laminate was exposed to UV-rays of a metal-halide lampunder the condition of an integrated amount of light of 1,000 mJ/cm² andas a result, the photo-curable adhesive sheet was cured. Thus an opticalinformation recording medium (DVD) was prepared.

Example 2

<Preparation of Photo-Curable Adhesive Sheet>

(Preparation of Reactive Polymer) Formulation I′ n-hexyl methacrylate 50parts by weight 2-hydroxyethyl methacrylate 50 parts by weightbenzophenone 5 parts by weight toluene 30 parts by weight ethyl acetate30 parts by weight

A mixture of the above Formulation I′ was heated to 60° C. withmoderately stirring to initiate the polymerization, and stirred at thistemperature for 10 hours to provide acrylic resin having a hydroxylgroup on its side chain. Then, 50 parts by weight of Calens MOI(2-isocyanatoethyl methacrylate; available from Showa Denko K.K.) wasadded to the solution of the acrylic resin, and reacted with each otherat 50° C. with moderately stirring to provide a solution 2 containing areactive polymer having a photopolymerizable functional group.

The resultant reactive polymer has Tg of 5° C., weight-average molecularweight of 130,000 and 50% by mole of methacryloyl group on its side.Formulation II′ solution 2 of reactive polymer 100 parts by weight1,6-hexanediol dimethacrylate 10 parts by weight 1-hydroxycyclohexylphenyl ketone 1 part by weight

The above Formulation II′ was homogeneously dissolved to give a mixture,which was applied onto a release sheet (thickness: 75 μm; trade name:No. 23, available from Fujimori Kogyo) and dried to form a photo-curableadhesive sheet of thickness of 25±2 μm. Thus, the resultantphoto-curable adhesive sheet had the release sheet and therefore thetotal thickness was 100±2 μm.

Preparation of One and the Other Optical Information RecordingSubstrates having Reflective Layer and Optical Information RecordingMedium

One and the other optical information recording substrates and opticalinformation recording medium were prepared in the same manner asdescribed in Example 1 except for using the above photo-curable adhesivesheet. Thus DVD was obtained.

Comparison Example 1

An optical information recording medium was prepared in the same manneras described in Example 1 except for performing the preparation of oneoptical information recording substrate and the recording medium in thefollowing manner:

Preparation of One Optical Information Recording Substrate havingReflective Layer

Melt carbonate was poured into a mold having an uneven surface as pitsand solidified to form an optical information recording substrate havingthickness of 100±2 μm. Silver alloy was spattered on the uneven surfaceof the optical information recording substrate to form a semitransparentreflective layer of silver alloy. Thus, one optical informationrecording substrate having reflective layer was prepared.

Preparation of Optical Information Recording Medium

A liquid curable adhesive (SD-661; available from DAINIPPON INK ANDCHEMICALS, INC.) which is commercially available was applied onto one ofthe two optical information recording substrates prepared above. The twooptical information recording substrates were bonded to each otherthrough the adhesive such that the two reflective layers faced eachother to give a laminate, and the laminate was exposed to UV-rayswhereby the adhesive sheet was cured. Thus an optical informationrecording medium (DVD) was prepared.

Evaluation of Optical Information Recording Substrate and Medium

(1) Light Transmittance (Wavelength of 380 to 800 nm)

Light transmittance of the resultant photo-curable adhesive sheet ismeasured in the wavelength of 380 to 800 nm according to JIS K6717.Light transmittance of 70% or more is marked as ◯, and Lighttransmittance of less than 70% is marked as X.

(2) Light Transmittance (wavelength of 380 to 420 nm)

Light transmittance of the resultant photo-curable adhesive sheet ismeasured in the wavelength of 380 to 420 nm according to JIS K6717.Light transmittance of 70% or more is marked as ◯, and Lighttransmittance of less than 70% is marked as X.

(3) Roughness of Land Portion

A land portion of an uneven surface on which pits were formed isevaluated on its smoothness using AFM (atomic force microscope). Landportion having sufficient smoothness is marked as ◯, and land portionhaving poor smoothness is marked as X.

(4) Readout of Signals

The information of the resultant optical information recording medium isread out using a laser beam of wavelength of 405 nm to obtain its wavypattern. This wavy pattern is compared with that of the stamper. Thewavy pattern of the medium coincident with that of the stamper is markedas ◯, and the wavy pattern of the medium little coincident with that ofthe stamper is marked as X.

The obtained results are shown in Table 1. TABLE 1 Example 1 Example 2Com. Example 1 Light transmittance ∘ ∘ ∘ (380-800 nm) Lighttransmittance ∘ ∘ ∘ (380-420 nm) Roughness of land ∘ ∘ x Readout ofsignals ∘ ∘ x

As shown above, the photo-curable adhesive sheet according to the firstaspect of the invention is depressed on an uneven shape of an opticalinformation recording substrate to precisely follow the uneven surfaceand adhere to it. Thus the resultant optical information recordingsubstrate has a signal surface (uneven surface) to which the adhesivelayer (sheet) precisely adheres, and is free from adverse effect on thesignal surface by the adhesion. Accordingly, the resultant opticalinformation recording medium scarcely brings about occurrence of errorswhen the information (signals) is read out.

Further, in the adhesion procedure in the preparation of the opticalinformation recording substrate of the invention, the photo-curableadhesive sheet used is softened and deformed and allowed to closelyadhere to the uneven surface, and then cured. Therefore, opticalinformation recording substrates can be bonded to each other by even athin layer having a thickness of 300 μm or less. Further, thephoto-curable adhesive sheet of the invention has high transparencycompared with conventional UV curable resin, and furthermore hasexcellent dimensional stability due to less cure shrinkage than aconventional UV-curable resin. Hence, the resultant optical informationrecording medium prepared using the adhesive sheet does not suffer fromdeformation such as warpage.

For example, the photo-curable adhesive sheet of the invention has asmall thickness (e.g., 25±2 μm, nonuniformity of ±2 μm) as an adhesivelayer, and therefore the adhesive sheet shows excellent precision in thethickness compared with that of an adhesive layer formed byspin-coat-application of a conventional UV curable resin liquid, theapplication bringing about thickness-nonuniformity of ±5 μm. Such lessthickness-nonuniformity can bring about enhancement of the dimensionalstability.

Since the photo-curable adhesive sheet of the invention has the aboveexcellent characteristics, it is apparent that the sheet is useful innot also the preparation of the resultant optical information recordingmedium but also the bonding operation in various fields.

Example 3

<Preparation of Photo-Curable Tranfer Sheet>

(Preparation of Reactive Polymer) Formulation I 2-ethylhexylmethacrylate 70 parts by weight methyl methacrylate 20 parts by weight2-hydroxyethyl methacrylate 10 parts by weight benzophenone 5 parts byweight toluene 30 parts by weight ethyl acetate 30 parts by weight

A mixture of the above Formulation I was heated to 60° C. withmoderately stirring to initiate the polymerization, and stirred at thistemperature for 10 hours to provide acrylic resin having a hydroxylgroup on its side chain. Then, 5 parts by weight of Calens MOI(2-isocyanatoethyl methacrylate; available from Showa Denko K.K.) wasadded to the solution of the acrylic resin, and reacted with each otherin an atmosphere of nitrogen at 50° C. with moderately stirring toprovide a solution 1 containing a reactive polymer having aphotopolymerizable functional group.

The resultant reactive polymer has Tg of 0° C., weight-average molecularweight of 150,000 and 5% by mole of methacryloyl group on its side.Formulation II solution 1 of reactive polymer 100 parts by weighttricyclodecane diacrylate 30 parts by weight 1-hydroxycyclohexyl phenylketone 1 part by weight

The above Formulation II was homogeneously dissolved to give a mixture,which was applied onto a release sheet (thickness: 75 μm; trade name:No. 23, available from Fujimori Kogyo) and dried to form a photo-curabletransfer sheet of thickness of 25±2 μm. Further, the above release sheetwas bonded onto a reverse side of the photo-curable transfer sheethaving release sheet.

Preparation of Optical Information Recording Medium

One of the release sheets of the photo-curable transfer sheet wasremoved. The photo-curable transfer sheet was disposed on an Alreflective layer (thickness: 70 nm) formed on an unevenness surface of apolycarbonate substrate (thickness: 1.1 mm) having the uneven surface aspits such that the surface having no release sheet faced the Alreflective layer, and the photo-curable transfer sheet was depressed onthe polycarbonate substrate using a roller made of silicone rubber underload of 2 kg to form a laminate (corresponding to the step of (2) inFIG. 6).

The other release sheet was removed from the resultant laminate. Astamper made of nickel and having an uneven surface as pits was disposedon an exposed surface of the transfer sheet of the laminate such thatthe uneven surface faced the exposed surface, and then the stamper wasdepressed on the laminate using a roller made of silicone rubber underload of 2 kg to form a laminate, whereby the uneven surface of thestamper was transferred to the surface of the transfer sheet.

Subsequently, the photo-curable transfer sheet of the laminate providedwith the stamper was exposed to UV-rays of a metal-halide lamp under thecondition of an integrated amount of light of 1,000 mJ/cm² and as aresult, the transferred photo-curable sheet was cured.

The stamper was removed from the laminate. Silver alloy was spattered onthe uneven surface of the cured photo-curable transfer sheet to form asemitransparent reflective layer of silver alloy. A polycarbonate film(thickness: 70 μm; Pure Ace C110-70, available from TEIJIN LTD.) wascontact bonded to the semitransparent reflective layer through anadhesive.

Thus, an optical information recording medium having two uneven surfaceswas prepared.

Example 4

<Preparation of Photo-Curable Tranfer Sheet>

(Preparation of Reactive Polymer) Formulation I′ n-hexyl methacrylate 50parts by weight 2-hydroxyethyl methacrylate 50 parts by weightbenzophenone 5 parts by weight toluene 30 parts by weight ethyl acetate30 parts by weight

A mixture of the above Formulation I′ was heated to 60° C. withmoderately stirring to initiate the polymerization, and stirred at thistemperature for 10 hours to provide acrylic resin having a hydroxylgroup on its side chain. Then, 50 parts by weight of Carends MOI(2-isocyanatoethyl methacrylate; available from Showa Denko K.K.) wasadded to the solution of the acrylic resin, and reacted with each otherin an atmosphere of nitrogen at 50° C. with moderately stirring toprovide a solution 2 containing a reactive polymer having aphotopolymerizable functional group.

The resultant reactive polymer has Tg of 5° C., weight-average molecularweight of 130,000 and 50% by mole of methacryloyl group on its side.Formulation II′ solution 2 of reactive polymer 100 parts by weight1,6-hexanediol dimethacrylate 10 parts by weight 1-hydroxycyclohexylphenyl ketone 1 part by weight

An above Formulation II′ was uniformly dissolved to give a mixture,which was applied onto a film of Pure Ace C110-70 (thickness: 70 μm;available from TEIJIN LTD.) and dried to form a photo-curable transfersheet of thickness of 30±2 μm. Thus, the resultant photo-curableadhesive sheet had the release sheet and therefore the total thicknesswas 100±2 μm.

Preparation of Optical Information Recording Medium

DVD was obtained in the same manner in Example 3 except for using theabove photo-curable transfer sheet having the film.

Comparison Example 2

Preparation of Optical Information Recording Medium

A liquid UV-curable adhesive (SD-661; available from DAINIPPON INK ANDCHEMICALS, INC.) was applied onto disposed on an Al reflective layer(thickness: 70 nm) formed on an unevenness surface of a polycarbonatesubstrate (thickness: 1.1 mm) having the uneven surface as pits, wherebya UV-curable resin layer A having a thickness of 10 μm was formed.

A liquid UV curable adhesive (SD-661; available from DAINIPPON INK ANDCHEMICALS, INC.) was applied onto disposed on an unevenness surface of astamper having the uneven surface as pits, whereby a UV curable resinlayer B having a thickness of 10 μm was formed.

The resultant substrate and the stamper were laminated on each othersuch that the UV curable resin layers A and B faced each other toprovide a laminate.

Subsequently, the UV curable resin layers A and B of the laminate wereexposed to UV-rays of a metal-halide lamp under the condition of anintegrated amount of light of 2,000 mJ/cm² and as a result, the resinlayers were cured.

The stamper was removed from the laminate. Silver alloy was spattered onthe uneven surface of the cured UV curable resin layers B to form asemitransparent reflective layer of silver alloy. A polycarbonate film(thickness: 70 μm; Pure Ace C110-70, available from TEIJIN LTD.) wasbonded to the semitransparent reflective layer through an adhesive.

Thus, an optical information recording medium having two uneven surfaceswas prepared.

Evaluation of Optical Information Recording Substrate and Medium

(1) Light Transmittance (Wavelength of 380 to 420 nm)

Light transmittance of one optical information recording substrate ismeasured in the wavelength of 380 to 420 nm according to JIS K6717.Light transmittance of 80% or more is marked as ◯, and Lighttransmittance of less than 80% is marked as X.

(2) Roughness of Land Portion

A land portion of a uneven surface on which pits were formed isevaluated on its smoothness using AFM (atomic force microscope). Landportion having sufficient smoothness is marked as ◯, and land portionhaving poor smoothness is marked as X.

(3) Readout of Signals

The information of the resultant optical information recording medium isread out using a laser beam of wavelength of 405 nm to obtain its wavypattern. This wavy pattern is compared with that of the stamper. Thewavy pattern of the medium coincident with that of the stamper is markedas ◯, and the wavy pattern of the medium little coincident with that ofthe stamper is marked as X.

The obtained results are shown in Table 2. TABLE 2 Example 3 Example 4Com. Example 2 Light transmittance ∘ ∘ ∘ (380-420 nm) Roughness of land∘ ∘ x Readout of signals ∘ ∘ x

The optical information recording medium obtained in Comparison Example2 has disadvantages of difficultly removing bubbles generated during thelaminating step, and of having poor transparency and increased warpage,compared with the media obtained in Examples 3 and 4. Therefore themedium of Comparison Example 2 is considered to be poor in the evaluatedcharacteristics.

As described above, by the process for the preparation of thephoto-curable transfer sheet according to the second aspect of theinvention, a further layer having an uneven surface can be formedextremely easily and in high productivity on an uneven surface of a discsubstrate. Further, the process of the invention permits an unevensurface of a disc substrate or a stamper to be easily and preciselytransferred to the transfer sheet without generation of bubbles. Thusthe resultant optical information recording substrate or medium has asignal surface (uneven surface) to which an uneven shape of a stamper orsubstrate is precisely transferred. Accordingly, an optical informationrecording medium prepared from the process scarcely brings aboutoccurrence of error when the information (signals) is read out.

Moreover, the process of the invention makes it possible to easily andprecisely cover an uneven surface of a disc substrate. Further, thephoto-curable transfer sheet used in the process of the invention hasexcellent dimension stability due to reduced shrinkage compared with aconventional UV-curable resin, and hence the process provides an opticalinformation recording medium free from deformation such as warpage.

Example 5

<Preparation of Photo-Curable Transfer Sheet>

(Preparation of Reactive Polymer) Formulation I 2-ethylhexylmethacrylate 70 parts by weight methyl methacrylate 20 parts by weight2-hydroxyethyl methacrylate 10 parts by weight benzophenone 5 parts byweight toluene 30 parts by weight ethyl acetate 30 parts by weight

A mixture of the above Formulation I was heated to 60° C. withmoderately stirring to initiate the polymerization, and stirred at thistemperature for 10 hours to provide acrylic resin having a hydroxylgroup on its side chain. Then, 5 parts by weight of Calens MOI(2-isocyanatoethyl methacrylate; available from Showa Denko K.K.) wasadded to the solution of the acrylic resin, and reacted with each otherat 50° C. with moderately stirring to provide a solution 1 containing areactive polymer having a photopolymerizable functional group.

The resultant reactive polymer has Tg of 0° C., weight-average molecularweight of 150,000 and 5% by mole of methacryloyl group on its side.Formulation II solution 1 of reactive polymer 100 parts by weighttricyclodecane diacrylate 30 parts by weight 1-hydroxycyclohexyl phenylketone 1 part by weight

The above Formulation II was homogeneously dissolved to give a mixture,which was applied onto a release sheet (surface roughness Ra=20 nm,available from Fujimori Kogyo) and dried. Thus, a photo-curable adhesivesheet having release sheet (surface roughness Ra=20 nm) of thickness of100±2 μm was prepared.

Preparation of One Optical Information Recording Substrate havingReflective Layer

The photo-curable transfer sheet was depressed on an unevenness surfaceof a stamper made of nickel having the uneven surface as pits using aroller made of silicone rubber under load of 2 kg to form a laminate inwhich the shape of the uneven surface was transferred to a surface ofthe photo-curable transfer sheet.

Subsequently, the photo-curable transfer sheet of the laminate wasexposed to UV-rays of a metal-halide lamp under the condition of anintegrated amount of light of 2,000 mJ/cm² and as a result, thetransferred layer (photo-curable sheet) was cured.

The stamper was peeled from the laminate. Silver alloy was spattered onthe uneven surface of the cured photo-curable layer (optical informationrecording substrate) to form a semitransparent reflective layer ofsilver alloy. Thus, an optical information recording substrate havingreflective layer was prepared.

Preparation of the Other Optical Information Recording Substrate havingReflective Layer

Melt carbonate was poured into a mold having an uneven surface as pitsand solidified to form an optical information recording substrate havingthickness of 1,100 μm. Aluminum was spattered on the uneven surface ofthe optical information recording substrate to form a reflective layerof Al. Thus, the other optical information recording substrate havingreflective layer was prepared.

Preparation of Optical Information Recording Medium

A liquid photo-curable adhesive (SD-661; available from DAINIPPON INKAND CHEMICALS, INC.), which is commercially available, was applied ontoone of the two optical information recording substrates prepared aboveby spin coating. The two optical information recording substrates werebonded to each other through the adhesive such that the two reflectivelayers faced each other to give a laminate, and the laminate was exposedto UV-rays whereby the adhesive was cured. Thus an optical informationrecording medium (DVD; surface roughness Ra=20 nm) was prepared.

Example 6

<Preparation of Photo-Curable Adhesive Sheet>

(Preparation of Reactive Polymer) Formulation I′ n-hexyl methacrylate 50parts by weight 2-hydroxyethyl methacrylate 50 parts by weightbenzophenone 5 parts by weight toluene 30 parts by weight ethyl acetate30 parts by weight

A mixture of the above Formulation I′ was heated to 60° C. withmoderately stirring to initiate the polymerization, and stirred at thistemperature for 10 hours to provide acrylic resin having a hydroxylgroup on its side chain. Then, 50 parts by weight of Calens MOI(2-isocyanatoethyl methacrylate; available from Showa Denko K.K.) wasadded to the solution of the acrylic resin, and reacted with each otherat 50° C. with moderately stirring to provide a solution 2 containing areactive polymer having a photopolymerizable functional group.

The resultant reactive polymer has Tg of 5C, weight-average molecularweight of 130,000 and 50% by mole of methacryloyl group on its side.Formulation II′ solution 2 of reactive polymer 100 parts by weight1,6-hexanediol dimethacrylate 10 parts by weight 1-hydroxycyclohexylphenyl ketone 1 part by weight

The above Formulation II′ was homogeneously dissolved to give a mixture,which was applied onto a release sheet (surface roughness Ra=2 nm,thickness: 70 μm; trade name: Pure Ace C110-70, available from TEIJINLTD.) and dried. Thus, a photo-curable adhesive sheet (surface roughnessRa=2 nm) having thickness of 100±2 μm was prepared.

Preparation of Optical Information Recording Medium

One and the other optical information recording substrates havingreflective layer and an optical information recording medium wereprepared in the same manner as Example 5 by using the resultant transfersheet. Thus an optical information recording medium (DVD; surfaceroughness Ra=2 nm) was prepared.

Comparison Example 3

The above Formulation I obtained in Example 5 was homogeneouslydissolved to give a mixture, which was applied onto a release sheet madeof polyester (surface roughness Ra=33 nm, thickness: 70 μm; availablefrom TEIJIN LTD.) and dried. Thus, a photo-curable adhesive sheet havingrelease sheet (surface roughness Ra=33 nm) of thickness of 100±2 μm wasprepared.

Subsequently, one and the other optical information recording substrateshaving reflective layer and an optical information recording medium wereprepared in the same manner as Example 5 by using the resultant transfersheet. Thus an optical information recording medium (DVD; surfaceroughness Ra=33 nm) was prepared.

Example 7

On the exposed surface (reproduction side) of the optical informationrecording medium obtained in Comparison Example 3, a hard-coat liquidsolution (Seikabeam VDAL292, available from) was applied by spincoating, and exposed to UV. Thus an optical information recording mediumwas prepared.

The surface roughness (Ra: center-line average roughness) of each ofExamples 5 to 7 and Comparison Examples 3 was determined below.

Measuring method of surface roughness:

Ra (center-line average roughness) of the sheet was measured by using acontact-type surface-roughness instrument (Talystep; available fromTaylor Hobson).

Evaluation of Optical Information Recording Substrate and Medium

(1) Light Transmittance (Wavelength of 380 to 420 nm)

Light transmittance of the resultant photo-curable adhesive sheet ismeasured in the wavelength of 380 to 420 nm according to JIS K6717.Light transmittance of 70% or more is marked as ◯, and Lighttransmittance of less than 70% is marked as X.

(2) Roughness of Land Portion

A land portion of an uneven surface on which pits were formed isevaluated on its smoothness using AFM (atomic force microscope). Landportion having sufficient smoothness is marked as ◯, and land portionhaving poor smoothness is marked as X.

(3) Readout of Signals

The information of the resultant optical information recording medium isread out using a laser beam of wavelength of 405 nm to obtain its wavypattern. This wavy pattern is compared with that of the stamper. Thewavy pattern of the medium coincident with that of the stamper is markedas ◯, and the wavy pattern of the medium little coincident with that ofthe stamper is marked as X.

The obtained results are shown in Table 3. TABLE 3 Example 5 Example 6Example 7 Co. Example 3 Light transmittance ∘ ∘ ∘ ∘ (380-420 nm)Roughness of land ∘ ∘ ∘ ∘ Readout of signals ∘ ∘ ∘ x

As shown above, the photo-curable transfer sheet according to the thirdaspect of the invention is depressed on an uneven shape of a stamper forpreparing an optical information recording substrate to precisely followthe uneven surface, and therefore the uneven surface is preciselytransferred to the surface of the transfer sheet, and simultaneously theadhesive sheet has an extremely smooth reverse surface having nounevenness. Thus the resultant optical information recording medium orsubstrate has a signal surface (uneven surface) to which the unevennessof the stamper has be precisely transferred and an extremely smoothreverse side (surface) corresponding to a laser-irradiation-side.Accordingly, the resultant optical information recording medium scarcelybrings about occurrence of errors when the information (signals) isrecorded or read out.

Further, the optical information recording medium or substrate obtainedby the invention is formed by deforming the photo-curable transfer sheetby melting and curing it to form an uneven surface, and therefore eventhe optical information recording substrate having a thickness of 300 μmor less can be prepared with excellent transferring.

Description of Reference Number

-   -   11: Photo-curable adhesive sheet    -   12 a, 12 b: Release sheet    -   23: Reflective layer    -   21, 24: Optical information recording substrate    -   25: Semitransparent reflective layer    -   51: Photo-curable transfer sheet    -   52 a, 52 b: Release sheet    -   61: Substrate    -   63: Reflective layer    -   64: Stamper    -   65: Silver alloy reflective layer (Semitransparent reflective        layer)    -   66: Organic polymer film (cover layer)    -   81: Photo-curable transfer sheet    -   82 a, 82 b: Release sheet    -   82 c: Support    -   83: Silver alloy reflective layer    -   90: Photo-curable transfer sheet having unevenness (optical        information recording substrate)    -   91: Stamper    -   100: Optical information recording substrate    -   110: Optical information recording medium    -   1, 2: Transparent resin substrate    -   1 a, 2 a: Reflective layer    -   3: Adhesive layer    -   1 b: Semitransparent layer

1. A photo-curable adhesive sheet comprising a photo-curable compositionwhich comprises a reactive polymer having a photopolymerizablefunctional group and weight-average molecular weight of not less than5,000 and which has a glass transition temperature of not more than 20°C., the photo-curable adhesive sheet having a light transmittance of notless than 70% in a wavelength range of 380 to 420 nm.
 2. Thephoto-curable adhesive sheet as defined in claim 1, wherein the reactivepolymer has a glass transition temperature of not more than 20° C. 3.The photo-curable adhesive sheet as defined in claim 1, which has alight transmittance of not less than 80% in a wavelength rang of 380 to420 nm.
 4. The photo-curable adhesive sheet as defined in claim 1,wherein the reactive polymer is an acrylic resin.
 5. The photo-curableadhesive sheet as defined in claim 1, wherein the reactive polymer has 1to 50% by mole of the photopolymerizable functional group.
 6. Thephoto-curable adhesive sheet as defined in claim 1, wherein thephotopolymerizable functional group is a (meth)acryloyl group.
 7. Thephoto-curable adhesive sheet as defined in claim 1, wherein thephoto-curable composition contains 0.1 to 10% by weight of aphotopolymerization initiator.
 8. The photo-curable adhesive sheet asdefined in claim 1, which has a thickness of 5 to 300 μm.
 9. Thephoto-curable adhesive sheet as defined in claim 1, wherein a releasesheet is provided on at least one side of the photo-curable adhesivesheet.
 10. A process for the preparation of an optical informationrecording medium comprising: superposing two optical informationrecording substrates having an uneven surface of recorded pits and/orgrooves on each other through the photo-curable adhesive sheet asdefined in claim 1 such that the two uneven surfaces face each other,depressing the substrates and the adhesive sheet to form a laminate, andcuring the laminate by light.
 11. The process as defined in claim 10,wherein the depressing step is carried out under reduced pressure. 12.The process as defined in claim 10 or 11, wherein the depressing step iscarried out at room temperature.
 13. A process for the preparation of anoptical information recording medium comprising: placing a photo-curabletransfer sheet comprising a photo-curable composition which comprises areactive polymer having a photopolymerizable functional group andweight-average molecular weight of not less than 5,000 and which iscapable of deforming by application of pressure on an opticalinformation recording substrate having an uneven surface of recordedpits and/or grooves such that one side of the photo-curable transfersheet is in contact with the uneven surface of the optical informationrecording substrate, depressing the sheet and substrate to form alaminate in which the one side of the photo-curable transfer sheetadheres closely to the uneven surface, and exposing the photo-curabletransfer sheet of the laminate to ultraviolet rays to cure the transfersheet.
 14. The process as defined in claim 13, the depressing step iscarried out under reduced pressure.
 15. The process as defined in claim13 or 14, wherein a reflective layer is provided on the uneven surfaceof the optical information recording substrate.
 16. A process for thepreparation of an optical information recording medium comprising:placing a photo-curable transfer sheet comprising a photo-curablecomposition which comprises a reactive polymer having aphotopolymerizable functional group and weight-average molecular weightof not less than 5,000 and which is capable of deforming by applicationof pressure on an optical information recording substrate having anuneven surface of recorded pits and/or grooves such that one side of thephoto-curable transfer sheet is in contact with the uneven surface ofthe optical information recording substrate, depressing the transfersheet and the substrate to allow the one side of the photo-curabletransfer sheet to adhere closely to the uneven surface, placing astamper having an uneven surface of recorded pits and/or grooves on thephoto-curable transfer sheet such that the uneven surface of the stamperis in contact with a side having no contact with the substrate of thephoto-curable transfer sheet, depressing the substrate, the transfersheet and the stamper to form a laminate in which the side of thephoto-curable transfer sheet adheres closely to the uneven surface ofthe stamper, exposing the photo-curable transfer sheet of the laminateto ultraviolet rays to cure the transfer sheet, and removing the stamperout of the laminate to form unevenness on a surface of the curedphoto-curable transfer sheet.
 17. The process as defined in claim 16,wherein an organic polymer film is further provided on the surfacehaving unevenness of the cured photo-curable transfer sheet through anadhesive layer.
 18. The process as defined in claim 16, wherein anotherphoto-curable transfer sheet is further depressed on the surface havingunevenness of the cured photo-curable transfer sheet and cured byirradiation of ultraviolet light.
 19. The process as defined in claim16, wherein the depressing step is carried out under reduced pressure.20. The process as defined in claim 16, wherein a reflective layer hasbeen provided on the unevenness surface of the substrate, and asemitransparent reflective layer is further provided on the surfacehaving unevenness of the cured photo-curable transfer sheet.
 21. Theprocess as defined in claim 13, wherein the photo-curable compositionhas a glass transition temperature of not more than 20° C.
 22. Theprocess as defined in claim 13, wherein the photo-curable transfer sheethas a light transmittance of not less than 70% in a wavelength range of380 to 420 nm.
 23. The process as defined in claim 13, wherein thephoto-curable transfer sheet has a thickness of 5 to 300 μm.
 24. Anoptical information recording medium prepared by the process as definedin claim 13 any of claims
 13. 25. A photo-curable transfer sheetcomprising a photo-curable composition which comprises a reactivepolymer having a photopolymerizable functional group and weight-averagemolecular weight of not less than 5,000 and which is capable ofdeforming by application of pressure, at least one side of thephoto-curable transfer sheet having a surface roughness (Ra) of not morethan 30 nm.
 26. The photo-curable transfer sheet as defined in claim 25,wherein the reactive polymer has a glass transition temperature of notmore than 20° C.
 27. The photo-curable transfer sheet as defined inclaim 25 or 26, wherein the surface roughness (Ra) of not more than 10nm.
 28. The photo-curable transfer sheet as defined in claim 25, whichhas a light transmittance of not less than 70% in a wavelength range of380 to 420 nm.
 29. The photo-curable transfer sheet as defined in claim25, which has a thickness of 5 to 300 μm.
 30. A process for thepreparation of a photo-curable transfer sheet as defined in claim 25comprising: melting a photo-curable composition which comprises areactive polymer having a photopolymerizable functional group andweight-average molecular weight of not less than 5,000 and which iscapable of deforming by application of pressure, and casting the meltedcomposition onto an surface of a support having a surface roughness (Ra)of not more than 30 nm.
 31. A process for the preparation of aphoto-curable transfer sheet as defined in claim 25 comprising: applyinga coating liquid containing a photo-curable composition which comprisesa reactive polymer having a photopolymerizable functional group andweight-average molecular weight of not less than 5,000 and which iscapable of deforming by application of pressure onto a surface of asupport having a surface roughness (Ra) of not more than 30 nm, anddrying a layer of the coating liquid.